Add accurate frame blending option

Cocoa/AppDelegate.m

@@ -1,5 +1,6 @@
 #import "AppDelegate.h"
 #include "GBButtons.h"
+#include "GBView.h"
 #include <Core/gb.h>
 #import <Carbon/Carbon.h>
 
@@ -36,6 +37,7 @@
                                                               @"GBColorCorrection": @(GB_COLOR_CORRECTION_EMULATE_HARDWARE),
                                                               @"GBHighpassFilter": @(GB_HIGHPASS_REMOVE_DC_OFFSET),
                                                               @"GBRewindLength": @(10),
+                                                              @"GBFrameBlendingMode": @([defaults boolForKey:@"DisableFrameBlending"]? GB_FRAME_BLENDING_MODE_DISABLED : GB_FRAME_BLENDING_MODE_ACCURATE),
                                                               
                                                               @"GBDMGModel": @(GB_MODEL_DMG_B),
                                                               @"GBCGBModel": @(GB_MODEL_CGB_E),

Cocoa/Document.m

@@ -492,7 +492,7 @@ static void audioCallback(GB_gameboy_t *gb, GB_sample_t *sample)
     
     self.consoleOutput.textContainerInset = NSMakeSize(4, 4);
     [self.view becomeFirstResponder];
-    self.view.shouldBlendFrameWithPrevious = ![[NSUserDefaults standardUserDefaults] boolForKey:@"DisableFrameBlending"];
+    self.view.frameBlendingMode = [[NSUserDefaults standardUserDefaults] integerForKey:@"GBFrameBlendingMode"];
     CGRect window_frame = self.mainWindow.frame;
     window_frame.size.width  = MAX([[NSUserDefaults standardUserDefaults] integerForKey:@"LastWindowWidth"],
                                   window_frame.size.width);
@@ -521,6 +521,11 @@ static void audioCallback(GB_gameboy_t *gb, GB_sample_t *sample)
                                                  name:@"GBColorCorrectionChanged"
                                                object:nil];
     
+    [[NSNotificationCenter defaultCenter] addObserver:self
+                                             selector:@selector(updateFrameBlendingMode)
+                                                 name:@"GBFrameBlendingModeChanged"
+                                               object:nil];
+    
     [[NSNotificationCenter defaultCenter] addObserver:self
                                              selector:@selector(updatePalette)
                                                  name:@"GBColorPaletteChanged"
@@ -677,12 +682,6 @@ static void audioCallback(GB_gameboy_t *gb, GB_sample_t *sample)
     [[NSUserDefaults standardUserDefaults] setBool:!self.audioClient.isPlaying forKey:@"Mute"];
 }
 
-- (IBAction)toggleBlend:(id)sender
-{
-    self.view.shouldBlendFrameWithPrevious ^= YES;
-    [[NSUserDefaults standardUserDefaults] setBool:!self.view.shouldBlendFrameWithPrevious forKey:@"DisableFrameBlending"];
-}
-
 - (BOOL)validateUserInterfaceItem:(id<NSValidatedUserInterfaceItem>)anItem
 {
     if([anItem action] == @selector(mute:)) {
@@ -695,9 +694,6 @@ static void audioCallback(GB_gameboy_t *gb, GB_sample_t *sample)
     else if ([anItem action] == @selector(reset:) && anItem.tag != MODEL_NONE) {
         [(NSMenuItem*)anItem setState:anItem.tag == current_model];
     }
-    else if ([anItem action] == @selector(toggleBlend:)) {
-        [(NSMenuItem*)anItem setState:self.view.shouldBlendFrameWithPrevious];
-    }
     else if ([anItem action] == @selector(interrupt:)) {
         if (![[NSUserDefaults standardUserDefaults] boolForKey:@"DeveloperMode"]) {
             return false;
@@ -1617,6 +1613,11 @@ static void audioCallback(GB_gameboy_t *gb, GB_sample_t *sample)
     }
 }
 
+- (void) updateFrameBlendingMode
+{
+    self.view.frameBlendingMode = (GB_frame_blending_mode_t) [[NSUserDefaults standardUserDefaults] integerForKey:@"GBFrameBlendingMode"];
+}
+
 - (void) updateRewindLength
 {
     [self performAtomicBlock:^{

Cocoa/GBGLShader.h

@@ -1,6 +1,7 @@
 #import <Foundation/Foundation.h>
+#import "GBView.h"
 
 @interface GBGLShader : NSObject
 - (instancetype)initWithName:(NSString *) shaderName;
-- (void) renderBitmap: (void *)bitmap previous:(void*) previous sized:(NSSize)srcSize inSize:(NSSize)dstSize scale: (double) scale;
+- (void) renderBitmap: (void *)bitmap previous:(void*) previous sized:(NSSize)srcSize inSize:(NSSize)dstSize scale: (double) scale withBlendingMode: (GB_frame_blending_mode_t)blendingMode;
 @end

Cocoa/GBGLShader.m

@@ -21,7 +21,7 @@ void main(void) {\n\
     GLuint resolution_uniform;
     GLuint texture_uniform;
     GLuint previous_texture_uniform;
-    GLuint mix_previous_uniform;
+    GLuint frame_blending_mode_uniform;
 
     GLuint position_attribute;
     GLuint texture;
@@ -70,7 +70,7 @@ void main(void) {\n\
         glBindTexture(GL_TEXTURE_2D, 0);
         previous_texture_uniform = glGetUniformLocation(program, "previous_image");
 
-        mix_previous_uniform = glGetUniformLocation(program, "mix_previous");
+        frame_blending_mode_uniform = glGetUniformLocation(program, "frame_blending_mode");
 
         // Configure OpenGL
         [self configureOpenGL];
@@ -79,7 +79,7 @@ void main(void) {\n\
     return self;
 }
 
-- (void) renderBitmap: (void *)bitmap previous:(void*) previous sized:(NSSize)srcSize inSize:(NSSize)dstSize scale: (double) scale
+- (void) renderBitmap: (void *)bitmap previous:(void*) previous sized:(NSSize)srcSize inSize:(NSSize)dstSize scale: (double) scale withBlendingMode:(GB_frame_blending_mode_t)blendingMode
 {
     glUseProgram(program);
     glUniform2f(resolution_uniform, dstSize.width * scale, dstSize.height * scale);
@@ -87,8 +87,8 @@ void main(void) {\n\
     glBindTexture(GL_TEXTURE_2D, texture);
     glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, srcSize.width, srcSize.height, 0, GL_RGBA, GL_UNSIGNED_BYTE, bitmap);
     glUniform1i(texture_uniform, 0);
-    glUniform1i(mix_previous_uniform, previous != NULL);
+    glUniform1i(frame_blending_mode_uniform, blendingMode);
-    if (previous) {
+    if (blendingMode) {
         glActiveTexture(GL_TEXTURE1);
         glBindTexture(GL_TEXTURE_2D, previous_texture);
         glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, srcSize.width, srcSize.height, 0, GL_RGBA, GL_UNSIGNED_BYTE, previous);

Cocoa/GBOpenGLView.m

@@ -14,10 +14,11 @@
     glViewport(0, 0, self.bounds.size.width * scale, self.bounds.size.height * scale);
     
     [self.shader renderBitmap:gbview.currentBuffer
-                     previous:gbview.shouldBlendFrameWithPrevious? gbview.previousBuffer : NULL
+                     previous:gbview.frameBlendingMode? gbview.previousBuffer : NULL
                         sized:NSMakeSize(GB_get_screen_width(gbview.gb), GB_get_screen_height(gbview.gb))
                        inSize:self.bounds.size
-                        scale:scale];
+                        scale:scale
+             withBlendingMode:gbview.frameBlendingMode];
     glFlush();
 }
 

Cocoa/GBPreferencesWindow.h

@@ -7,6 +7,7 @@
 @property (strong) IBOutlet NSButton *aspectRatioCheckbox;
 @property (strong) IBOutlet NSPopUpButton *highpassFilterPopupButton;
 @property (strong) IBOutlet NSPopUpButton *colorCorrectionPopupButton;
+@property (strong) IBOutlet NSPopUpButton *frameBlendingModePopupButton;
 @property (strong) IBOutlet NSPopUpButton *colorPalettePopupButton;
 @property (strong) IBOutlet NSPopUpButton *displayBorderPopupButton;
 @property (strong) IBOutlet NSPopUpButton *rewindPopupButton;

Cocoa/GBPreferencesWindow.m

@@ -14,6 +14,7 @@
     NSPopUpButton *_graphicsFilterPopupButton;
     NSPopUpButton *_highpassFilterPopupButton;
     NSPopUpButton *_colorCorrectionPopupButton;
+    NSPopUpButton *_frameBlendingModePopupButton;
     NSPopUpButton *_colorPalettePopupButton;
     NSPopUpButton *_displayBorderPopupButton;
     NSPopUpButton *_rewindPopupButton;
@@ -87,6 +88,18 @@
     return _colorCorrectionPopupButton;
 }
 
+- (void)setFrameBlendingModePopupButton:(NSPopUpButton *)frameBlendingModePopupButton
+{
+    _frameBlendingModePopupButton = frameBlendingModePopupButton;
+    NSInteger mode = [[NSUserDefaults standardUserDefaults] integerForKey:@"GBFrameBlendingMode"];
+    [_frameBlendingModePopupButton selectItemAtIndex:mode];
+}
+
+- (NSPopUpButton *)frameBlendingModePopupButton
+{
+    return _frameBlendingModePopupButton;
+}
+
 - (void)setColorPalettePopupButton:(NSPopUpButton *)colorPalettePopupButton
 {
     _colorPalettePopupButton = colorPalettePopupButton;
@@ -223,7 +236,14 @@
     [[NSUserDefaults standardUserDefaults] setObject:@([sender indexOfSelectedItem])
                                               forKey:@"GBColorCorrection"];
     [[NSNotificationCenter defaultCenter] postNotificationName:@"GBColorCorrectionChanged" object:nil];
+}
 
+- (IBAction)franeBlendingModeChanged:(id)sender
+{
+    [[NSUserDefaults standardUserDefaults] setObject:@([sender indexOfSelectedItem])
+                                              forKey:@"GBFrameBlendingMode"];
+    [[NSNotificationCenter defaultCenter] postNotificationName:@"GBFrameBlendingModeChanged" object:nil];
+    
 }
 
 - (IBAction)colorPaletteChanged:(id)sender
@@ -231,7 +251,6 @@
     [[NSUserDefaults standardUserDefaults] setObject:@([sender indexOfSelectedItem])
                                               forKey:@"GBColorPalette"];
     [[NSNotificationCenter defaultCenter] postNotificationName:@"GBColorPaletteChanged" object:nil];
-    
 }
 
 - (IBAction)displayBorderChanged:(id)sender
@@ -239,7 +258,6 @@
     [[NSUserDefaults standardUserDefaults] setObject:@([sender selectedItem].tag)
                                               forKey:@"GBBorderMode"];
     [[NSNotificationCenter defaultCenter] postNotificationName:@"GBBorderModeChanged" object:nil];
-    
 }
 
 - (IBAction)rewindLengthChanged:(id)sender

Cocoa/GBView.h

@@ -2,11 +2,19 @@
 #include <Core/gb.h>
 #import "GBJoystickListener.h"
 
+typedef enum {
+    GB_FRAME_BLENDING_MODE_DISABLED,
+    GB_FRAME_BLENDING_MODE_SIMPLE,
+    GB_FRAME_BLENDING_MODE_ACCURATE,
+    GB_FRAME_BLENDING_MODE_ACCURATE_EVEN = GB_FRAME_BLENDING_MODE_ACCURATE,
+    GB_FRAME_BLENDING_MODE_ACCURATE_ODD,
+} GB_frame_blending_mode_t;
+
 @interface GBView<GBJoystickListener> : NSView
 - (void) flip;
 - (uint32_t *) pixels;
 @property GB_gameboy_t *gb;
-@property (nonatomic) BOOL shouldBlendFrameWithPrevious;
+@property (nonatomic) GB_frame_blending_mode_t frameBlendingMode;
 @property (getter=isMouseHidingEnabled) BOOL mouseHidingEnabled;
 @property bool isRewinding;
 @property NSView *internalView;

Cocoa/GBView.m

@@ -19,6 +19,7 @@
     bool underclockKeyDown;
     double clockMultiplier;
     NSEventModifierFlags previousModifiers;
+    GB_frame_blending_mode_t _frameBlendingMode;
 }
 
 + (instancetype)alloc
@@ -43,8 +44,7 @@
 }
 
 - (void) _init
-{    
+{
-    _shouldBlendFrameWithPrevious = 1;
     [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(ratioKeepingChanged) name:@"GBAspectChanged" object:nil];
     tracking_area = [ [NSTrackingArea alloc] initWithRect:(NSRect){}
                                                   options:NSTrackingMouseEnteredAndExited | NSTrackingActiveAlways | NSTrackingInVisibleRect
@@ -79,15 +79,26 @@
     [self setFrame:self.superview.frame];
 }
 
-- (void) setShouldBlendFrameWithPrevious:(BOOL)shouldBlendFrameWithPrevious
+- (void) setFrameBlendingMode:(GB_frame_blending_mode_t)frameBlendingMode
 {
-    _shouldBlendFrameWithPrevious = shouldBlendFrameWithPrevious;
+    _frameBlendingMode = frameBlendingMode;
     [self setNeedsDisplay:YES];
 }
 
+
+- (GB_frame_blending_mode_t)frameBlendingMode
+{
+    if (_frameBlendingMode == GB_FRAME_BLENDING_MODE_ACCURATE) {
+        if (GB_is_sgb(_gb)) {
+            return GB_FRAME_BLENDING_MODE_SIMPLE;
+        }
+        return GB_is_odd_frame(_gb)? GB_FRAME_BLENDING_MODE_ACCURATE_ODD : GB_FRAME_BLENDING_MODE_ACCURATE_EVEN;
+    }
+    return _frameBlendingMode;
+}
 - (unsigned char) numberOfBuffers
 {
-    return _shouldBlendFrameWithPrevious? 3 : 2;
+    return _frameBlendingMode? 3 : 2;
 }
 
 - (void)dealloc

Cocoa/GBViewMetal.m

@@ -15,7 +15,7 @@ static const vector_float2 rect[] =
     id<MTLBuffer> vertices;
     id<MTLRenderPipelineState> pipeline_state;
     id<MTLCommandQueue> command_queue;
-    id<MTLBuffer> mix_previous_buffer;
+    id<MTLBuffer> frame_blending_mode_buffer;
     id<MTLBuffer> output_resolution_buffer;
     vector_float2 output_resolution;
 }
@@ -23,7 +23,7 @@ static const vector_float2 rect[] =
 + (bool)isSupported
 {
     if (MTLCopyAllDevices) {
-        return [MTLCopyAllDevices() count];
+        return false; //[MTLCopyAllDevices() count];
     }
     return false;
 }
@@ -56,10 +56,10 @@ static const vector_float2 rect[] =
                                    length:sizeof(rect)
                                   options:MTLResourceStorageModeShared];
     
-    static const bool default_mix_value = false;
+    static const GB_frame_blending_mode_t default_blending_mode = GB_FRAME_BLENDING_MODE_DISABLED;
-    mix_previous_buffer = [device newBufferWithBytes:&default_mix_value
+    frame_blending_mode_buffer = [device newBufferWithBytes:&default_blending_mode
-                                              length:sizeof(default_mix_value)
+                                          length:sizeof(default_blending_mode)
-                                             options:MTLResourceStorageModeShared];
+                                         options:MTLResourceStorageModeShared];
     
     output_resolution_buffer = [device newBufferWithBytes:&output_resolution
                                                    length:sizeof(output_resolution)
@@ -147,7 +147,7 @@ static const vector_float2 rect[] =
                mipmapLevel:0
                  withBytes:[self currentBuffer]
                bytesPerRow:texture.width * 4];
-    if ([self shouldBlendFrameWithPrevious]) {
+    if ([self frameBlendingMode]) {
         [previous_texture replaceRegion:region
                             mipmapLevel:0
                               withBytes:[self previousBuffer]
@@ -157,9 +157,9 @@ static const vector_float2 rect[] =
     MTLRenderPassDescriptor *render_pass_descriptor = view.currentRenderPassDescriptor;
     id<MTLCommandBuffer> command_buffer = [command_queue commandBuffer];
 
-    if(render_pass_descriptor != nil)
+    if (render_pass_descriptor != nil)
     {
-        *(bool *)[mix_previous_buffer contents] = [self shouldBlendFrameWithPrevious];
+        *(GB_frame_blending_mode_t *)[frame_blending_mode_buffer contents] = [self frameBlendingMode];
         *(vector_float2 *)[output_resolution_buffer contents] = output_resolution;
 
         id<MTLRenderCommandEncoder> render_encoder =
@@ -176,7 +176,7 @@ static const vector_float2 rect[] =
                                  offset:0
                                 atIndex:0];
         
-        [render_encoder setFragmentBuffer:mix_previous_buffer
+        [render_encoder setFragmentBuffer:frame_blending_mode_buffer
                                    offset:0
                                   atIndex:0];
         

Cocoa/Preferences.xib

@@ -69,6 +69,7 @@
                 <outlet property="delegate" destination="-2" id="ASc-vN-Zbq"/>
                 <outlet property="displayBorderPopupButton" destination="R9D-FV-bpd" id="VfO-b4-gqH"/>
                 <outlet property="dmgPopupButton" destination="LFw-Uk-cPR" id="KDw-i2-k4u"/>
+                <outlet property="frameBlendingModePopupButton" destination="lxk-db-Sxv" id="wzt-uo-TE6"/>
                 <outlet property="graphicsFilterPopupButton" destination="6pP-kK-EEC" id="LS7-HY-kHC"/>
                 <outlet property="highpassFilterPopupButton" destination="T69-6N-dhT" id="0p6-4m-hb1"/>
                 <outlet property="playerListButton" destination="gWx-7h-0xq" id="zo6-82-JId"/>
@@ -80,11 +81,11 @@
             <point key="canvasLocation" x="183" y="354"/>
         </window>
         <customView id="sRK-wO-K6R">
-            <rect key="frame" x="0.0" y="0.0" width="292" height="267"/>
+            <rect key="frame" x="0.0" y="0.0" width="292" height="323"/>
             <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMinY="YES"/>
             <subviews>
                 <textField horizontalHuggingPriority="251" verticalHuggingPriority="750" fixedFrame="YES" translatesAutoresizingMaskIntoConstraints="NO" id="T91-rh-rRp">
-                    <rect key="frame" x="18" y="230" width="256" height="17"/>
+                    <rect key="frame" x="18" y="286" width="256" height="17"/>
                     <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMinY="YES"/>
                     <textFieldCell key="cell" scrollable="YES" lineBreakMode="clipping" sendsActionOnEndEditing="YES" title="Graphics filter:" id="pXg-WY-8Q5">
                         <font key="font" metaFont="system"/>
@@ -93,7 +94,7 @@
                     </textFieldCell>
                 </textField>
                 <popUpButton verticalHuggingPriority="750" fixedFrame="YES" translatesAutoresizingMaskIntoConstraints="NO" id="6pP-kK-EEC">
-                    <rect key="frame" x="30" y="198" width="234" height="26"/>
+                    <rect key="frame" x="30" y="254" width="234" height="26"/>
                     <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMinY="YES"/>
                     <popUpButtonCell key="cell" type="push" title="Nearest neighbor (Pixelated)" bezelStyle="rounded" alignment="left" lineBreakMode="truncatingTail" state="on" borderStyle="borderAndBezel" imageScaling="proportionallyDown" inset="2" selectedItem="neN-eo-LA7" id="I1w-05-lGl">
                         <behavior key="behavior" lightByBackground="YES" lightByGray="YES"/>
@@ -130,7 +131,7 @@
                     </connections>
                 </popUpButton>
                 <textField horizontalHuggingPriority="251" verticalHuggingPriority="750" fixedFrame="YES" translatesAutoresizingMaskIntoConstraints="NO" id="Wc3-2K-6CD">
-                    <rect key="frame" x="18" y="176" width="256" height="17"/>
+                    <rect key="frame" x="18" y="232" width="256" height="17"/>
                     <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMinY="YES"/>
                     <textFieldCell key="cell" scrollable="YES" lineBreakMode="clipping" sendsActionOnEndEditing="YES" title="Color correction:" id="5Si-hz-EK3">
                         <font key="font" metaFont="system"/>
@@ -139,7 +140,7 @@
                     </textFieldCell>
                 </textField>
                 <popUpButton verticalHuggingPriority="750" fixedFrame="YES" translatesAutoresizingMaskIntoConstraints="NO" id="VEz-N4-uP6">
-                    <rect key="frame" x="30" y="144" width="234" height="26"/>
+                    <rect key="frame" x="30" y="200" width="234" height="26"/>
                     <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMinY="YES"/>
                     <popUpButtonCell key="cell" type="push" title="Disabled" bezelStyle="rounded" alignment="left" lineBreakMode="truncatingTail" state="on" borderStyle="borderAndBezel" imageScaling="proportionallyDown" inset="2" selectedItem="D2J-wV-1vu" id="fNJ-Fi-yOm">
                         <behavior key="behavior" lightByBackground="YES" lightByGray="YES"/>
@@ -160,6 +161,35 @@
                         <action selector="colorCorrectionChanged:" target="QvC-M9-y7g" id="Oq4-B5-nO6"/>
                     </connections>
                 </popUpButton>
+                <textField horizontalHuggingPriority="251" verticalHuggingPriority="750" fixedFrame="YES" translatesAutoresizingMaskIntoConstraints="NO" id="MLC-Rx-FgO">
+                    <rect key="frame" x="20" y="178" width="252" height="17"/>
+                    <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMinY="YES"/>
+                    <textFieldCell key="cell" scrollable="YES" lineBreakMode="clipping" sendsActionOnEndEditing="YES" title="Frame blending" id="UCa-EO-tzh">
+                        <font key="font" metaFont="system"/>
+                        <color key="textColor" name="labelColor" catalog="System" colorSpace="catalog"/>
+                        <color key="backgroundColor" name="controlColor" catalog="System" colorSpace="catalog"/>
+                    </textFieldCell>
+                </textField>
+                <popUpButton verticalHuggingPriority="750" fixedFrame="YES" translatesAutoresizingMaskIntoConstraints="NO" id="lxk-db-Sxv">
+                    <rect key="frame" x="32" y="149" width="229" height="22"/>
+                    <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMinY="YES"/>
+                    <popUpButtonCell key="cell" type="push" title="Disabled" bezelStyle="rounded" alignment="left" lineBreakMode="truncatingTail" state="on" borderStyle="borderAndBezel" imageScaling="proportionallyDown" inset="2" selectedItem="iHP-Yz-fiH" id="aQ6-HN-7Aj">
+                        <behavior key="behavior" lightByBackground="YES" lightByGray="YES"/>
+                        <font key="font" metaFont="menu"/>
+                        <menu key="menu" id="Q9L-qo-kF4">
+                            <items>
+                                <menuItem title="Disabled" state="on" id="iHP-Yz-fiH">
+                                    <modifierMask key="keyEquivalentModifierMask"/>
+                                </menuItem>
+                                <menuItem title="Simple" id="Hxy-jw-x6E"/>
+                                <menuItem title="Accurate" id="Aaq-uy-Csa"/>
+                            </items>
+                        </menu>
+                    </popUpButtonCell>
+                    <connections>
+                        <action selector="franeBlendingModeChanged:" target="QvC-M9-y7g" id="kE1-pm-MIp"/>
+                    </connections>
+                </popUpButton>
                 <textField horizontalHuggingPriority="251" verticalHuggingPriority="750" fixedFrame="YES" translatesAutoresizingMaskIntoConstraints="NO" id="8fG-zm-hpr">
                     <rect key="frame" x="18" y="122" width="252" height="17"/>
                     <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMinY="YES"/>
@@ -231,7 +261,7 @@
                     </connections>
                 </button>
             </subviews>
-            <point key="canvasLocation" x="-176" y="639.5"/>
+            <point key="canvasLocation" x="-176" y="667.5"/>
         </customView>
         <customView id="ymk-46-SX7">
             <rect key="frame" x="0.0" y="0.0" width="292" height="320"/>
@@ -460,7 +490,7 @@
                     <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMinY="YES"/>
                     <clipView key="contentView" focusRingType="none" ambiguous="YES" drawsBackground="NO" id="AMs-PO-nid">
                         <rect key="frame" x="1" y="1" width="238" height="209"/>
-                        <autoresizingMask key="autoresizingMask"/>
+                        <autoresizingMask key="autoresizingMask" widthSizable="YES" heightSizable="YES"/>
                         <subviews>
                             <tableView focusRingType="none" appearanceType="vibrantLight" verticalHuggingPriority="750" allowsExpansionToolTips="YES" columnAutoresizingStyle="lastColumnOnly" columnReordering="NO" columnResizing="NO" multipleSelection="NO" emptySelection="NO" autosaveColumns="NO" typeSelect="NO" id="UDd-IJ-fxX">
                                 <rect key="frame" x="0.0" y="0.0" width="238" height="209"/>

Core/display.c

@@ -797,6 +797,8 @@ void GB_display_run(GB_gameboy_t *gb, uint8_t cycles)
         return;
     }
     
+    gb->is_odd_frame = false;
+    
     if (!GB_is_cgb(gb)) {
         GB_SLEEP(gb, display, 23, 1);
     }
@@ -1228,6 +1230,7 @@ abort_fetching_object:
                     }
                     else {
                         if (!GB_is_sgb(gb) || gb->current_lcd_line < LINES) {
+                            gb->is_odd_frame ^= true;
                             display_vblank(gb);
                         }
                         gb->frame_skip_state = GB_FRAMESKIP_SECOND_FRAME_RENDERED;
@@ -1236,6 +1239,7 @@ abort_fetching_object:
                 else {
                     gb->frame_skip_state = GB_FRAMESKIP_SECOND_FRAME_RENDERED;
                     if (!GB_is_sgb(gb) || gb->current_lcd_line < LINES) {
+                        gb->is_odd_frame ^= true;
                         display_vblank(gb);
                     }
                 }
@@ -1465,3 +1469,9 @@ uint8_t GB_get_oam_info(GB_gameboy_t *gb, GB_oam_info_t *dest, uint8_t *sprite_h
     }
     return count;
 }
+
+
+bool GB_is_odd_frame(GB_gameboy_t *gb)
+{
+    return gb->is_odd_frame;
+}

Core/display.h

@@ -58,4 +58,5 @@ void GB_draw_tilemap(GB_gameboy_t *gb, uint32_t *dest, GB_palette_type_t palette
 uint8_t GB_get_oam_info(GB_gameboy_t *gb, GB_oam_info_t *dest, uint8_t *sprite_height);
 uint32_t GB_convert_rgb15(GB_gameboy_t *gb, uint16_t color, bool for_border);
 void GB_set_color_correction_mode(GB_gameboy_t *gb, GB_color_correction_mode_t mode);
+bool GB_is_odd_frame(GB_gameboy_t *gb);
 #endif /* display_h */

Core/gb.h

@@ -524,6 +524,7 @@ struct GB_gameboy_internal_s {
         bool wy_triggered;
         uint8_t window_tile_x;
         uint8_t lcd_x; // The LCD can go out of sync since the push signal is skipped in some cases.
+        bool is_odd_frame;
     );
 
     /* Unsaved data. This includes all pointers, as well as everything that shouldn't be on a save state */

SDL/gui.c

@@ -46,9 +46,22 @@ void render_texture(void *pixels,  void *previous)
         }
         glClearColor(0, 0, 0, 1);
         glClear(GL_COLOR_BUFFER_BIT);
+        GB_frame_blending_mode_t mode = configuration.blending_mode;
+        if (!previous) {
+            mode = GB_FRAME_BLENDING_MODE_DISABLED;
+        }
+        else if (mode == GB_FRAME_BLENDING_MODE_ACCURATE) {
+            if (GB_is_sgb(&gb)) {
+                mode = GB_FRAME_BLENDING_MODE_SIMPLE;
+            }
+            else {
+                mode = GB_is_odd_frame(&gb)? GB_FRAME_BLENDING_MODE_ACCURATE_ODD : GB_FRAME_BLENDING_MODE_ACCURATE_EVEN;
+            }
+        }
         render_bitmap_with_shader(&shader, _pixels, previous,
                                   GB_get_screen_width(&gb), GB_get_screen_height(&gb),
-                                  rect.x, rect.y, rect.w, rect.h);
+                                  rect.x, rect.y, rect.w, rect.h,
+                                  mode);
         SDL_GL_SwapWindow(window);
     }
 }
@@ -91,7 +104,7 @@ configuration_t configuration =
     .color_correction_mode = GB_COLOR_CORRECTION_EMULATE_HARDWARE,
     .highpass_mode = GB_HIGHPASS_ACCURATE,
     .scaling_mode = GB_SDL_SCALING_INTEGER_FACTOR,
-    .blend_frames = true,
+    .blending_mode = GB_FRAME_BLENDING_MODE_ACCURATE,
     .rewind_length = 60 * 2,
     .model = MODEL_CGB
 };
@@ -600,23 +613,39 @@ const char *current_filter_name(unsigned index)
     return shaders[i].display_name;
 }
 
-static void toggle_blend_frames(unsigned index)
+static void cycle_blending_mode(unsigned index)
 {
-    configuration.blend_frames ^= true;
+    if (configuration.blending_mode == GB_FRAME_BLENDING_MODE_ACCURATE) {
+        configuration.blending_mode = GB_FRAME_BLENDING_MODE_DISABLED;
+    }
+    else {
+        configuration.blending_mode++;
+    }
 }
 
-const char *blend_frames_string(unsigned index)
+static void cycle_blending_mode_backwards(unsigned index)
 {
-    return configuration.blend_frames? "Enabled" : "Disabled";
+    if (configuration.blending_mode == GB_FRAME_BLENDING_MODE_DISABLED) {
+        configuration.blending_mode = GB_FRAME_BLENDING_MODE_ACCURATE;
+    }
+    else {
+        configuration.blending_mode--;
+    }
+}
+
+const char *blending_mode_string(unsigned index)
+{
+    return (const char *[]){"Disabled", "Simple", "Accurate"}
+    [configuration.blending_mode];
 }
 
 static const struct menu_item graphics_menu[] = {
     {"Scaling Mode:", cycle_scaling, current_scaling_mode, cycle_scaling_backwards},
     {"Scaling Filter:", cycle_filter, current_filter_name, cycle_filter_backwards},
     {"Color Correction:", cycle_color_correction, current_color_correction_mode, cycle_color_correction_backwards},
+    {"Frame Blending:", cycle_blending_mode, blending_mode_string, cycle_blending_mode_backwards},
     {"Mono Palette:", cycle_palette, current_palette, cycle_palette_backwards},
     {"Display Border:", cycle_border_mode, current_border_mode, cycle_border_mode_backwards},
-    {"Blend Frames:", toggle_blend_frames, blend_frames_string, toggle_blend_frames},
     {"Back", return_to_root_menu},
     {NULL,}
 };

SDL/gui.h

@@ -70,7 +70,7 @@ typedef struct {
     SDL_Scancode keys[9];
     GB_color_correction_mode_t color_correction_mode;
     enum scaling_mode scaling_mode;
-    bool blend_frames;
+    uint8_t blending_mode;
     
     GB_highpass_mode_t highpass_mode;
     

SDL/main.c

@@ -372,7 +372,7 @@ static void vblank(GB_gameboy_t *gb)
         clock_mutliplier += 1.0/16;
         GB_set_clock_multiplier(gb, clock_mutliplier);
     }
-    if (configuration.blend_frames) {
+    if (configuration.blending_mode) {
         render_texture(active_pixel_buffer, previous_pixel_buffer);
         uint32_t *temp = active_pixel_buffer;
         active_pixel_buffer = previous_pixel_buffer;

SDL/shader.c

@@ -130,7 +130,7 @@ bool init_shader_with_name(shader_t *shader, const char *name)
     glBindTexture(GL_TEXTURE_2D, 0);
     shader->previous_texture_uniform = glGetUniformLocation(shader->program, "previous_image");
     
-    shader->mix_previous_uniform = glGetUniformLocation(shader->program, "mix_previous");
+    shader->blending_mode_uniform = glGetUniformLocation(shader->program, "frame_blending_mode");
     
     // Program
     
@@ -164,7 +164,8 @@ bool init_shader_with_name(shader_t *shader, const char *name)
 
 void render_bitmap_with_shader(shader_t *shader, void *bitmap, void *previous,
                                unsigned source_width, unsigned source_height,
-                               unsigned x, unsigned y, unsigned w, unsigned h)
+                               unsigned x, unsigned y, unsigned w, unsigned h,
+                               GB_frame_blending_mode_t blending_mode)
 {
     glUseProgram(shader->program);
     glUniform2f(shader->origin_uniform, x, y);
@@ -173,7 +174,7 @@ void render_bitmap_with_shader(shader_t *shader, void *bitmap, void *previous,
     glBindTexture(GL_TEXTURE_2D, shader->texture);
     glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, source_width, source_height, 0, GL_RGBA, GL_UNSIGNED_BYTE, bitmap);
     glUniform1i(shader->texture_uniform, 0);
-    glUniform1i(shader->mix_previous_uniform, previous != NULL);
+    glUniform1i(shader->blending_mode_uniform, previous? blending_mode : GB_FRAME_BLENDING_MODE_DISABLED);
     if (previous) {
         glActiveTexture(GL_TEXTURE1);
         glBindTexture(GL_TEXTURE_2D, shader->previous_texture);

SDL/shader.h

@@ -8,7 +8,7 @@ typedef struct shader_s {
     GLuint origin_uniform;
     GLuint texture_uniform;
     GLuint previous_texture_uniform;
-    GLuint mix_previous_uniform;
+    GLuint blending_mode_uniform;
     
     GLuint position_attribute;
     GLuint texture;
@@ -16,10 +16,19 @@ typedef struct shader_s {
     GLuint program;
 } shader_t;
 
+typedef enum {
+    GB_FRAME_BLENDING_MODE_DISABLED,
+    GB_FRAME_BLENDING_MODE_SIMPLE,
+    GB_FRAME_BLENDING_MODE_ACCURATE,
+    GB_FRAME_BLENDING_MODE_ACCURATE_EVEN = GB_FRAME_BLENDING_MODE_ACCURATE,
+    GB_FRAME_BLENDING_MODE_ACCURATE_ODD,
+} GB_frame_blending_mode_t;
+
 bool init_shader_with_name(shader_t *shader, const char *name);
 void render_bitmap_with_shader(shader_t *shader, void *bitmap, void *previous,
                                unsigned source_width, unsigned source_height,
-                               unsigned x, unsigned y, unsigned w, unsigned h);
+                               unsigned x, unsigned y, unsigned w, unsigned h,
+                               GB_frame_blending_mode_t blending_mode);
 void free_shader(struct shader_s *shader);
 
 #endif /* shader_h */

Shaders/MasterShader.fsh

@@ -1,7 +1,7 @@
 #version 150
 uniform sampler2D image;
 uniform sampler2D previous_image;
-uniform bool mix_previous;
+uniform int frame_blending_mode;
 
 uniform vec2 output_resolution;
 uniform vec2 origin;
@@ -15,6 +15,15 @@ out vec4 frag_color;
 #line 1
 {filter}
 
+
+#define BLEND_BIAS (1.0/3.0)
+
+#define DISABLED 0
+#define SIMPLE 1
+#define ACCURATE 2
+#define ACCURATE_EVEN ACCURATE
+#define ACCURATE_ODD 3
+
 void main()
 {
     vec2 position = gl_FragCoord.xy - origin;
@@ -22,11 +31,34 @@ void main()
     position.y = 1 - position.y;
     vec2 input_resolution = textureSize(image, 0);
 
-    if (mix_previous) {
+    float ratio;
-        frag_color = mix(scale(image, position, input_resolution, output_resolution),
+    switch (frame_blending_mode) {
-                         scale(previous_image, position, input_resolution, output_resolution), 0.5);
+        default:
-    }
+        case DISABLED:
-    else {
+            frag_color = scale(image, position, input_resolution, output_resolution);
-        frag_color = scale(image, position, input_resolution, output_resolution);
+            return;
+        case SIMPLE:
+            ratio = 0.5;
+            break;
+        case ACCURATE_EVEN:
+            if ((int(position.y * input_resolution.y) & 1) == 0) {
+                ratio = BLEND_BIAS;
+            }
+            else {
+                ratio = 1 - BLEND_BIAS;
+            }
+            break;
+        case ACCURATE_ODD:
+            if ((int(position.y * input_resolution.y) & 1) == 0) {
+                ratio = 1 - BLEND_BIAS;
+            }
+            else {
+                ratio = BLEND_BIAS;
+            }
+            break;
     }
+
+    frag_color = mix(scale(image, position, input_resolution, output_resolution),
+                     scale(previous_image, position, input_resolution, output_resolution), ratio);
+
 }

Shaders/MasterShader.metal

@@ -42,19 +42,52 @@ static inline float4 texture(texture2d<half> texture, float2 pos)
 #line 1
 {filter}
 
+#define BLEND_BIAS (1.0/3.0)
+
+enum frame_blending_mode {
+    DISABLED,
+    SIMPLE,
+    ACCURATE,
+    ACCURATE_EVEN = ACCURATE,
+    ACCURATE_ODD,
+};
+
 fragment float4 fragment_shader(rasterizer_data in [[stage_in]],
                                 texture2d<half> image [[ texture(0) ]],
                                 texture2d<half> previous_image [[ texture(1) ]],
-                                constant bool *mix_previous [[ buffer(0) ]],
+                                constant enum frame_blending_mode *frame_blending_mode [[ buffer(0) ]],
                                 constant float2 *output_resolution [[ buffer(1) ]])
 {
     float2 input_resolution = float2(image.get_width(), image.get_height());
 
     in.texcoords.y = 1 - in.texcoords.y;
-    if (*mix_previous) {
+    float ratio;
-        return mix(scale(image, in.texcoords, input_resolution, *output_resolution),
+    switch (*frame_blending_mode) {
-                   scale(previous_image, in.texcoords, input_resolution, *output_resolution), 0.5);
+        default:
+        case DISABLED:
+            return scale(image, in.texcoords, input_resolution, *output_resolution);
+        case SIMPLE:
+            ratio = 0.5;
+            break;
+        case ACCURATE_EVEN:
+            if (((int)(in.texcoords.y * input_resolution.y) & 1) == 0) {
+                ratio = BLEND_BIAS;
+            }
+            else {
+                ratio = 1 - BLEND_BIAS;
+            }
+            break;
+        case ACCURATE_ODD:
+            if (((int)(in.texcoords.y * input_resolution.y) & 1) == 0) {
+                ratio = 1 - BLEND_BIAS;
+            }
+            else {
+                ratio = BLEND_BIAS;
+            }
+            break;
     }
-    return scale(image, in.texcoords, input_resolution, *output_resolution);
+    
+    return mix(scale(image, in.texcoords, input_resolution, *output_resolution),
+               scale(previous_image, in.texcoords, input_resolution, *output_resolution), ratio);
 }