Filter support for Cocoa port + 7 basic filters

Cocoa/AppDelegate.m

@@ -24,6 +24,8 @@
                                                               @"GBStart": @"\r",
 
                                                               @"GBTurbo": @" ",
+
+                                                              @"GBFilter": @"NearestNeighbor",
                                                               }];
 #undef KEY
 }

Cocoa/Document.m

@@ -41,7 +41,7 @@ static char *consoleInput(GB_gameboy_t *gb)
 
 static uint32_t rgbEncode(GB_gameboy_t *gb, unsigned char r, unsigned char g, unsigned char b)
 {
-    return (r << 24) | (g << 16) | (b << 8);
+    return (r << 0) | (g << 8) | (b << 16);
 }
 
 @implementation Document

Cocoa/GBPreferencesWindow.h

@@ -2,4 +2,5 @@
 
 @interface GBPreferencesWindow : NSWindow <NSTableViewDelegate, NSTableViewDataSource>
 @property IBOutlet NSTableView *controlsTableView;
+@property IBOutlet NSPopUpButton *graphicsFilterPopupButton;
 @end

Cocoa/GBPreferencesWindow.m

@@ -6,6 +6,38 @@
 {
     bool is_button_being_modified;
     NSInteger button_being_modified;
+
+    NSPopUpButton *_graphicsFilterPopupButton;
+}
+
++ (NSArray *)filterList
+{
+    /* The filter list as ordered in the popup button */
+    static NSArray * filters = nil;
+    if (!filters) {
+        filters = @[
+                    @"NearestNeighbor",
+                    @"Bilinear",
+                    @"SmoothBilinear",
+                    @"Scale2x",
+                    @"Scale4x",
+                    @"AAScale2x",
+                    @"AAScale4x",
+                    ];
+    }
+    return filters;
+}
+
+- (NSPopUpButton *)graphicsFilterPopupButton
+{
+    return _graphicsFilterPopupButton;
+}
+
+- (void)setGraphicsFilterPopupButton:(NSPopUpButton *)graphicsFilterPopupButton
+{
+    _graphicsFilterPopupButton = graphicsFilterPopupButton;
+    NSString *filter = [[NSUserDefaults standardUserDefaults] objectForKey:@"GBFilter"];
+    [_graphicsFilterPopupButton selectItemAtIndex:[[[self class] filterList] indexOfObject:filter]];
 }
 
 - (NSInteger)numberOfRowsInTableView:(NSTableView *)tableView
@@ -56,5 +88,12 @@
     [self.controlsTableView reloadData];
     [self makeFirstResponder:self.controlsTableView];
 }
+- (IBAction)graphicFilterChanged:(NSPopUpButton *)sender
+{
+
+    [[NSUserDefaults standardUserDefaults] setObject:[[self class] filterList][[sender indexOfSelectedItem]]
+                                              forKey:@"GBFilter"];
+    [[NSNotificationCenter defaultCenter] postNotificationName:@"GBFilterChanged" object:nil];
+}
 
 @end

Cocoa/GBShader.h

@@ -0,0 +1,6 @@
+#import <Foundation/Foundation.h>
+
+@interface GBShader : NSObject
+- (instancetype)initWithName:(NSString *) shaderName;
+- (void) renderBitmap: (void *)bitmap previous:(void*) previous inSize:(NSSize)size scale: (double) scale;
+@end

Cocoa/GBShader.m

@@ -0,0 +1,170 @@
+#import "GBShader.h"
+#import <OpenGL/gl.h>
+
+/*
+ Loosely based of https://www.raywenderlich.com/70208/opengl-es-pixel-shaders-tutorial
+ */
+
+static NSString * const vertex_shader = @"\n\
+attribute vec2 aPosition;\n\
+\n\
+void main(void) {\n\
+    gl_Position = vec4(aPosition, 0., 1.);\n\
+}\n\
+";
+
+@implementation GBShader
+{
+    GLuint resolution_uniform;
+    GLuint texture_uniform;
+    GLuint previous_texture_uniform;
+    GLuint mix_previous_uniform;
+
+    GLuint position_attribute;
+    GLuint texture;
+    GLuint previous_texture;
+    GLuint program;
+}
+
++ (NSString *) shaderSourceForName:(NSString *) name
+{
+    return [NSString stringWithContentsOfFile:[[NSBundle mainBundle] pathForResource:name
+                                                                              ofType:@"fsh"
+                                                                         inDirectory:@"Shaders"]
+                                     encoding:NSUTF8StringEncoding
+                                        error:nil];
+}
+
+- (instancetype)initWithName:(NSString *) shaderName
+{
+    self = [super init];
+    if (self) {
+        // Program
+        NSString *fragment_shader = [[self class] shaderSourceForName:@"MasterShader"];
+        fragment_shader = [fragment_shader stringByReplacingOccurrencesOfString:@"\n" withString:@""];
+        fragment_shader = [fragment_shader stringByReplacingOccurrencesOfString:@"{filter}"
+                                                                     withString:[[self class] shaderSourceForName:shaderName]];
+        program = [[self class] programWithVertexShader:vertex_shader fragmentShader:fragment_shader];
+        // Attributes
+        position_attribute = glGetAttribLocation(program, "aPosition");
+        // Uniforms
+        resolution_uniform = glGetUniformLocation(program, "uResolution");
+
+        glGenTextures(1, &texture);
+        glBindTexture(GL_TEXTURE_2D, texture);
+        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+        glBindTexture(GL_TEXTURE_2D, 0);
+        texture_uniform = glGetUniformLocation(program, "image");
+
+        glGenTextures(1, &previous_texture);
+        glBindTexture(GL_TEXTURE_2D, previous_texture);
+        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+        glBindTexture(GL_TEXTURE_2D, 0);
+        previous_texture_uniform = glGetUniformLocation(program, "previousImage");
+
+        mix_previous_uniform = glGetUniformLocation(program, "uMixPrevious");
+
+        // Configure OpenGL ES
+        [self configureOpenGLES];
+    }
+    return self;
+}
+
+- (void) renderBitmap: (void *)bitmap previous:(void*) previous inSize:(NSSize)size scale: (double) scale
+{
+    glUseProgram(program);
+    glUniform2f(resolution_uniform, size.width * scale, size.height * scale);
+    glActiveTexture(GL_TEXTURE0);
+    glBindTexture(GL_TEXTURE_2D, texture);
+    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 160, 144, 0, GL_RGBA, GL_UNSIGNED_BYTE, bitmap);
+    glUniform1i(texture_uniform, 0);
+    glUniform1i(mix_previous_uniform, previous != NULL);
+    if (previous) {
+        glActiveTexture(GL_TEXTURE1);
+        glBindTexture(GL_TEXTURE_2D, previous_texture);
+        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 160, 144, 0, GL_RGBA, GL_UNSIGNED_BYTE, previous);
+        glUniform1i(previous_texture_uniform, 1);
+    }
+    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+}
+
+- (void)configureOpenGLES
+{
+    // Program
+    glUseProgram(program);
+
+    // Attributes
+    glEnableVertexAttribArray(position_attribute);
+    static GLfloat const quad[8] = {
+        -1.f, -1.f,
+        -1.f, +1.f,
+        +1.f, -1.f,
+        +1.f, +1.f,
+    };
+    glVertexAttribPointer(position_attribute, 2, GL_FLOAT, GL_FALSE, 0, quad);
+}
+
++ (GLuint)programWithVertexShader:(NSString*)vsh fragmentShader:(NSString*)fsh
+{
+    // Build shaders
+    GLuint vertex_shader = [self shaderWithContents:vsh type:GL_VERTEX_SHADER];
+    GLuint fragment_shader = [self shaderWithContents:fsh type:GL_FRAGMENT_SHADER];
+    // Create program
+    GLuint program = glCreateProgram();
+    // Attach shaders
+    glAttachShader(program, vertex_shader);
+    glAttachShader(program, fragment_shader);
+    // Link program
+    glLinkProgram(program);
+    // Check for errors
+    GLint status;
+    glGetProgramiv(program, GL_LINK_STATUS, &status);
+    if (status == GL_FALSE) {
+        GLchar messages[1024];
+        glGetProgramInfoLog(program, sizeof(messages), 0, &messages[0]);
+        NSLog(@"%@:- GLSL Program Error: %s", self, messages);
+    }
+
+    // Delete shaders
+    glDeleteShader(vertex_shader);
+    glDeleteShader(fragment_shader);
+
+    return program;
+}
+
+- (void)dealloc
+{
+    glDeleteProgram(program);
+    glDeleteTextures(1, &texture);
+    glDeleteTextures(1, &previous_texture);
+}
+
++ (GLuint)shaderWithContents:(NSString*)contents type:(GLenum)type
+{
+
+    const GLchar* source = [contents UTF8String];
+    // Create the shader object
+    GLuint shader = glCreateShader(type);
+    // Load the shader source
+    glShaderSource(shader, 1, &source, 0);
+    // Compile the shader
+    glCompileShader(shader);
+    // Check for errors
+    GLint status = 0;
+    glGetShaderiv(shader, GL_COMPILE_STATUS, &status);
+    if (status == GL_FALSE) {
+        GLchar messages[1024];
+        glGetShaderInfoLog(shader, sizeof(messages), 0, &messages[0]);
+        NSLog(@"%@:- GLSL Shader Error: %s", self, messages);
+    }
+
+    return shader;
+}
+
+@end

Cocoa/GBView.h

@@ -1,4 +1,5 @@
 #import <Cocoa/Cocoa.h>
+#import "GBShader.h"
 #include "gb.h"
 
 @interface GBView : NSOpenGLView
@@ -6,4 +7,5 @@
 - (uint32_t *) pixels;
 @property GB_gameboy_t *gb;
 @property BOOL shouldBlendFrameWithPrevious;
+@property GBShader *shader;
 @end

Cocoa/GBView.m

@@ -3,6 +3,8 @@
 #import "GBButtons.h"
 #import "NSString+StringForKey.h"
 
+static GBShader *shader = nil;
+
 @implementation GBView
 {
     uint32_t *image_buffers[3];
@@ -15,6 +17,12 @@
     image_buffers[1] = malloc(160 * 144 * 4);
     image_buffers[2] = malloc(160 * 144 * 4);
     _shouldBlendFrameWithPrevious = 1;
+    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(filterChanged) name:@"GBFilterChanged" object:nil];
+}
+
+- (void) filterChanged
+{
+    self.shader = nil;
 }
 
 - (unsigned char) numberOfBuffers
@@ -27,6 +35,7 @@
     free(image_buffers[0]);
     free(image_buffers[1]);
     free(image_buffers[2]);
+    [[NSNotificationCenter defaultCenter] removeObserver:self];
 }
 - (instancetype)initWithCoder:(NSCoder *)coder
 {
@@ -49,16 +58,21 @@
 }
 
 - (void)drawRect:(NSRect)dirtyRect {
+    if (!self.shader) {
+        self.shader = [[GBShader alloc] initWithName:[[NSUserDefaults standardUserDefaults] objectForKey:@"GBFilter"]];
+    }
     double scale = self.window.backingScaleFactor;
-    glRasterPos2d(-1, 1);
-    glPixelZoom(self.bounds.size.width / 160 * scale, self.bounds.size.height / -144 * scale);
-    glDrawPixels(160, 144, GL_ABGR_EXT, GL_UNSIGNED_BYTE, image_buffers[current_buffer]);
     if (_shouldBlendFrameWithPrevious) {
-        glEnable(GL_BLEND);
+        [self.shader renderBitmap:image_buffers[current_buffer]
-        glBlendFunc(GL_CONSTANT_ALPHA, GL_ONE_MINUS_CONSTANT_ALPHA);
+                         previous:image_buffers[(current_buffer + 2) % self.numberOfBuffers]
-        glBlendColor(1, 1, 1, 0.5);
+                           inSize:self.bounds.size
-        glDrawPixels(160, 144, GL_ABGR_EXT, GL_UNSIGNED_BYTE, image_buffers[(current_buffer + 2) % self.numberOfBuffers]);
+                            scale:scale];
-        glDisable(GL_BLEND);
+    }
+    else {
+        [self.shader renderBitmap:image_buffers[current_buffer]
+                         previous:NULL
+                           inSize:self.bounds.size
+                            scale:scale];
     }
     glFlush();
 }

Cocoa/Preferences.xib

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
-<document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="9531" systemVersion="14F1509" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES" customObjectInstantitationMethod="direct">
+<document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="9531" systemVersion="14F1713" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES" customObjectInstantitationMethod="direct">
     <dependencies>
         <plugIn identifier="com.apple.InterfaceBuilder.CocoaPlugin" version="9531"/>
     </dependencies>
@@ -14,11 +14,11 @@
         <window title="Preferences" allowsToolTipsWhenApplicationIsInactive="NO" autorecalculatesKeyViewLoop="NO" oneShot="NO" releasedWhenClosed="NO" animationBehavior="default" id="QvC-M9-y7g" customClass="GBPreferencesWindow">
             <windowStyleMask key="styleMask" titled="YES" closable="YES"/>
             <windowPositionMask key="initialPositionMask" leftStrut="YES" rightStrut="YES" topStrut="YES" bottomStrut="YES"/>
-            <rect key="contentRect" x="196" y="240" width="292" height="237"/>
+            <rect key="contentRect" x="196" y="240" width="292" height="292"/>
             <rect key="screenRect" x="0.0" y="0.0" width="2560" height="1417"/>
             <view key="contentView" id="EiT-Mj-1SZ">
-                <rect key="frame" x="0.0" y="0.0" width="292" height="237"/>
+                <rect key="frame" x="0.0" y="0.0" width="292" height="292"/>
-                <autoresizingMask key="autoresizingMask"/>
+                <autoresizingMask key="autoresizingMask" widthSizable="YES" heightSizable="YES"/>
                 <subviews>
                     <textField horizontalHuggingPriority="251" verticalHuggingPriority="750" fixedFrame="YES" translatesAutoresizingMaskIntoConstraints="NO" id="Utu-t4-cLx">
                         <rect key="frame" x="18" y="201" width="256" height="17"/>
@@ -28,6 +28,39 @@
                             <color key="backgroundColor" name="controlColor" catalog="System" colorSpace="catalog"/>
                         </textFieldCell>
                     </textField>
+                    <textField horizontalHuggingPriority="251" verticalHuggingPriority="750" fixedFrame="YES" translatesAutoresizingMaskIntoConstraints="NO" id="T91-rh-rRp">
+                        <rect key="frame" x="18" y="255" width="256" height="17"/>
+                        <textFieldCell key="cell" scrollable="YES" lineBreakMode="clipping" sendsActionOnEndEditing="YES" title="Graphics Filter:" id="pXg-WY-8Q5">
+                            <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="6pP-kK-EEC">
+                        <rect key="frame" x="30" y="223" width="245" height="26"/>
+                        <popUpButtonCell key="cell" type="push" bezelStyle="rounded" alignment="left" lineBreakMode="truncatingTail" borderStyle="borderAndBezel" imageScaling="proportionallyDown" inset="2" id="I1w-05-lGl">
+                            <behavior key="behavior" lightByBackground="YES" lightByGray="YES"/>
+                            <font key="font" metaFont="system"/>
+                            <menu key="menu" id="xDC-0T-Qg9">
+                                <items>
+                                    <menuItem title="Nearest Neighbor (Pixelated)" id="neN-eo-LA7">
+                                        <modifierMask key="keyEquivalentModifierMask"/>
+                                    </menuItem>
+                                    <menuItem title="Bilinear (Blurry)" id="iDe-si-atu"/>
+                                    <menuItem title="Smooth Bilinear (Less blurry)" id="1jN-pO-1iD"/>
+                                    <menuItem title="Scale2x" id="C1I-L2-Up1"/>
+                                    <menuItem title="Scale4x" id="uWA-Zp-JY9"/>
+                                    <menuItem title="Anti-aliased Scale2x" id="iP6-DJ-CVH"/>
+                                    <menuItem title="Anti-aliased Scale4x" id="zJR-ER-Ygo">
+                                        <modifierMask key="keyEquivalentModifierMask"/>
+                                    </menuItem>
+                                </items>
+                            </menu>
+                        </popUpButtonCell>
+                        <connections>
+                            <action selector="graphicFilterChanged:" target="QvC-M9-y7g" id="n87-t4-fbV"/>
+                        </connections>
+                    </popUpButton>
                     <scrollView focusRingType="none" fixedFrame="YES" autohidesScrollers="YES" horizontalLineScroll="19" horizontalPageScroll="10" verticalLineScroll="19" verticalPageScroll="10" hasHorizontalScroller="NO" hasVerticalScroller="NO" usesPredominantAxisScrolling="NO" horizontalScrollElasticity="none" verticalScrollElasticity="none" translatesAutoresizingMaskIntoConstraints="NO" id="PBp-dj-EIa">
                         <rect key="frame" x="20" y="20" width="252" height="173"/>
                         <clipView key="contentView" focusRingType="none" ambiguous="YES" drawsBackground="NO" id="AMs-PO-nid">
@@ -90,8 +123,9 @@
             <connections>
                 <outlet property="controlsTableView" destination="UDd-IJ-fxX" id="a1D-Md-yXv"/>
                 <outlet property="delegate" destination="-2" id="ASc-vN-Zbq"/>
+                <outlet property="graphicsFilterPopupButton" destination="6pP-kK-EEC" id="LS7-HY-kHC"/>
             </connections>
-            <point key="canvasLocation" x="179" y="403.5"/>
+            <point key="canvasLocation" x="179" y="431"/>
         </window>
     </objects>
 </document>

Makefile

@@ -67,6 +67,8 @@ $(OBJ)/%.m.o: %.m
 
 # Cocoa Port
 
+Shaders:$(shell echo Shaders/*.fsh)
+
 $(BIN)/Sameboy.app: $(BIN)/Sameboy.app/Contents/MacOS/Sameboy \
 					$(shell echo Cocoa/*.icns) \
 					Cocoa/License.html \
@@ -75,11 +77,14 @@ $(BIN)/Sameboy.app: $(BIN)/Sameboy.app/Contents/MacOS/Sameboy \
 					$(BIN)/BootROMs/cgb_boot.bin \
 					$(BIN)/Sameboy.app/Contents/Resources/Base.lproj/Document.nib \
 					$(BIN)/Sameboy.app/Contents/Resources/Base.lproj/MainMenu.nib \
-					$(BIN)/Sameboy.app/Contents/Resources/Base.lproj/Preferences.nib
+					$(BIN)/Sameboy.app/Contents/Resources/Base.lproj/Preferences.nib \
+					Shaders
 	mkdir -p $(BIN)/Sameboy.app/Contents/Resources
 	cp Cocoa/*.icns $(BIN)/BootROMs/dmg_boot.bin $(BIN)/BootROMs/cgb_boot.bin $(BIN)/Sameboy.app/Contents/Resources/
 	sed s/@VERSION/$(VERSION)/ < Cocoa/info.plist > $(BIN)/Sameboy.app/Contents/info.plist
 	cp Cocoa/License.html $(BIN)/Sameboy.app/Contents/Resources/Credits.html
+	mkdir -p $(BIN)/Sameboy.app/Contents/Resources/Shaders
+	cp Shaders/*.fsh $(BIN)/Sameboy.app/Contents/Resources/Shaders
 
 $(BIN)/Sameboy.app/Contents/MacOS/Sameboy: $(CORE_OBJECTS) $(COCOA_OBJECTS)
 	-@mkdir -p $(dir $@)

Shaders/AAScale2x.fsh

@@ -0,0 +1,47 @@
+vec4 scale2x(sampler2D image)
+{
+    // o = offset, the width of a pixel
+    vec2 o = 1.0 / textureDimensions;
+    vec2 texCoord = vec2(gl_FragCoord.x, uResolution.y - gl_FragCoord.y) / uResolution;
+
+    // texel arrangement
+    // A B C
+    // D E F
+    // G H I
+    vec4 A = texture2D(image, texCoord + vec2( -o.x,  o.y));
+    vec4 B = texture2D(image, texCoord + vec2(    0,  o.y));
+    vec4 C = texture2D(image, texCoord + vec2(  o.x,  o.y));
+    vec4 D = texture2D(image, texCoord + vec2( -o.x,    0));
+    vec4 E = texture2D(image, texCoord + vec2(    0,    0));
+    vec4 F = texture2D(image, texCoord + vec2(  o.x,    0));
+    vec4 G = texture2D(image, texCoord + vec2( -o.x, -o.y));
+    vec4 H = texture2D(image, texCoord + vec2(    0, -o.y));
+    vec4 I = texture2D(image, texCoord + vec2(  o.x, -o.y));
+    vec2 p = texCoord * textureDimensions;
+    // p = the position within a pixel [0...1]
+    p = fract(p);
+    if (p.x > .5) {
+        if (p.y > .5) {
+            // Top Right
+            return B == F && B != D && F != H ? F : E;
+        } else {
+            // Bottom Right
+            return H == F && D != H && B != F ? F : E;
+        }
+    } else {
+        if (p.y > .5) {
+            // Top Left
+            return D == B && B != F && D != H ? D : E;
+        } else {
+            // Bottom Left
+            return D == H && D != B && H != F ? D : E;
+        }
+    }
+}
+
+vec4 filter(sampler2D image)
+{
+    vec2 texCoord = vec2(gl_FragCoord.x, uResolution.y - gl_FragCoord.y) / uResolution;
+
+    return mix(texture2D(image, texCoord), scale2x(image), 0.5);
+}

Shaders/AAScale4x.fsh

@@ -0,0 +1,87 @@
+vec4 scale2x(sampler2D image, vec2 texCoord)
+{
+    // o = offset, the width of a pixel
+    vec2 o = 1.0 / textureDimensions;
+    // texel arrangement
+    // A B C
+    // D E F
+    // G H I
+    vec4 A = texture2D(image, texCoord + vec2( -o.x,  o.y));
+    vec4 B = texture2D(image, texCoord + vec2(    0,  o.y));
+    vec4 C = texture2D(image, texCoord + vec2(  o.x,  o.y));
+    vec4 D = texture2D(image, texCoord + vec2( -o.x,    0));
+    vec4 E = texture2D(image, texCoord + vec2(    0,    0));
+    vec4 F = texture2D(image, texCoord + vec2(  o.x,    0));
+    vec4 G = texture2D(image, texCoord + vec2( -o.x, -o.y));
+    vec4 H = texture2D(image, texCoord + vec2(    0, -o.y));
+    vec4 I = texture2D(image, texCoord + vec2(  o.x, -o.y));
+    vec2 p = texCoord * textureDimensions;
+    // p = the position within a pixel [0...1]
+    p = fract(p);
+    if (p.x > .5) {
+        if (p.y > .5) {
+            // Top Right
+            return B == F && B != D && F != H ? F : E;
+        } else {
+            // Bottom Right
+            return H == F && D != H && B != F ? F : E;
+        }
+    } else {
+        if (p.y > .5) {
+            // Top Left
+            return D == B && B != F && D != H ? D : E;
+        } else {
+            // Bottom Left
+            return D == H && D != B && H != F ? D : E;
+        }
+    }
+}
+
+vec4 aaScale2x(sampler2D image, vec2 texCoord)
+{
+    return mix(texture2D(image, texCoord), scale2x(image, texCoord), 0.5);
+}
+
+vec4 filter(sampler2D image)
+{
+    // o = offset, the width of a pixel
+    vec2 o = 1.0 / (textureDimensions * 2.);
+    vec2 texCoord = vec2(gl_FragCoord.x, uResolution.y - gl_FragCoord.y) / uResolution;
+
+    // texel arrangement
+    // A B C
+    // D E F
+    // G H I
+    vec4 A = aaScale2x(image, texCoord + vec2( -o.x,  o.y));
+    vec4 B = aaScale2x(image, texCoord + vec2(    0,  o.y));
+    vec4 C = aaScale2x(image, texCoord + vec2(  o.x,  o.y));
+    vec4 D = aaScale2x(image, texCoord + vec2( -o.x,    0));
+    vec4 E = aaScale2x(image, texCoord + vec2(    0,    0));
+    vec4 F = aaScale2x(image, texCoord + vec2(  o.x,    0));
+    vec4 G = aaScale2x(image, texCoord + vec2( -o.x, -o.y));
+    vec4 H = aaScale2x(image, texCoord + vec2(    0, -o.y));
+    vec4 I = aaScale2x(image, texCoord + vec2(  o.x, -o.y));
+    vec4 R;
+    vec2 p = texCoord * textureDimensions * 2.;
+    // p = the position within a pixel [0...1]
+    p = fract(p);
+    if (p.x > .5) {
+        if (p.y > .5) {
+            // Top Right
+            R = B == F && B != D && F != H ? F : E;
+        } else {
+            // Bottom Right
+            R = H == F && D != H && B != F ? F : E;
+        }
+    } else {
+        if (p.y > .5) {
+            // Top Left
+            R = D == B && B != F && D != H ? D : E;
+        } else {
+            // Bottom Left
+            R = D == H && D != B && H != F ? D : E;
+        }
+    }
+
+    return mix(R, E, 0.5);
+}

Shaders/Bilinear.fsh

@@ -0,0 +1,16 @@
+vec4 filter(sampler2D image)
+{
+    vec2 texCoord = vec2(gl_FragCoord.x, uResolution.y - gl_FragCoord.y) / uResolution;
+
+    vec2 pixel = texCoord * textureDimensions;
+
+    vec4 q11 = texture2D(image, vec2(floor(pixel.x) / textureDimensions.x, floor(pixel.y) / textureDimensions.y));
+    vec4 q12 = texture2D(image, vec2(floor(pixel.x) / textureDimensions.x, ceil(pixel.y) / textureDimensions.y));
+    vec4 q21 = texture2D(image, vec2(ceil(pixel.x) / textureDimensions.x, floor(pixel.y) / textureDimensions.y));
+    vec4 q22 = texture2D(image, vec2(ceil(pixel.x) / textureDimensions.x, ceil(pixel.y) / textureDimensions.y));
+
+    vec4 r1 = mix(q11, q21, fract(pixel.x));
+    vec4 r2 = mix(q12, q22, fract(pixel.x));
+
+    return mix (r1, r2, fract(pixel.y));
+}

Shaders/MasterShader.fsh

@@ -0,0 +1,17 @@
+uniform sampler2D image;
+uniform sampler2D previousImage;
+uniform bool uMixPrevious;
+
+uniform vec2 uResolution;
+const vec2 textureDimensions = vec2(160, 144);
+
+{filter}
+
+void main() {
+    if (uMixPrevious) {
+        gl_FragColor = mix(filter(image), filter(previousImage), 0.5);
+    }
+    else {
+        gl_FragColor = filter(image);
+    }
+}

Shaders/NearestNeighbor.fsh

@@ -0,0 +1,6 @@
+vec4 filter(sampler2D image)
+{
+    vec2 texCoord = vec2(gl_FragCoord.x, uResolution.y - gl_FragCoord.y) / uResolution;
+
+    return texture2D(image, texCoord);
+}

Shaders/Scale2x.fsh

@@ -0,0 +1,42 @@
+/* Shader implementation of Scale2x is adapted from https://gist.github.com/singron/3161079 */
+
+vec4 filter(sampler2D image)
+{
+    // o = offset, the width of a pixel
+    vec2 o = 1.0 / textureDimensions;
+    vec2 texCoord = vec2(gl_FragCoord.x, uResolution.y - gl_FragCoord.y) / uResolution;
+
+    // texel arrangement
+    // A B C
+    // D E F
+    // G H I
+    vec4 A = texture2D(image, texCoord + vec2( -o.x,  o.y));
+    vec4 B = texture2D(image, texCoord + vec2(    0,  o.y));
+    vec4 C = texture2D(image, texCoord + vec2(  o.x,  o.y));
+    vec4 D = texture2D(image, texCoord + vec2( -o.x,    0));
+    vec4 E = texture2D(image, texCoord + vec2(    0,    0));
+    vec4 F = texture2D(image, texCoord + vec2(  o.x,    0));
+    vec4 G = texture2D(image, texCoord + vec2( -o.x, -o.y));
+    vec4 H = texture2D(image, texCoord + vec2(    0, -o.y));
+    vec4 I = texture2D(image, texCoord + vec2(  o.x, -o.y));
+    vec2 p = texCoord * textureDimensions;
+    // p = the position within a pixel [0...1]
+    p = fract(p);
+    if (p.x > .5) {
+        if (p.y > .5) {
+            // Top Right
+            return B == F && B != D && F != H ? F : E;
+        } else {
+            // Bottom Right
+            return H == F && D != H && B != F ? F : E;
+        }
+    } else {
+        if (p.y > .5) {
+            // Top Left
+            return D == B && B != F && D != H ? D : E;
+        } else {
+            // Bottom Left
+            return D == H && D != B && H != F ? D : E;
+        }
+    }
+}

Shaders/Scale4x.fsh

@@ -0,0 +1,80 @@
+vec4 scale2x(sampler2D image, vec2 texCoord)
+{
+    // o = offset, the width of a pixel
+    vec2 o = 1.0 / textureDimensions;
+    // texel arrangement
+    // A B C
+    // D E F
+    // G H I
+    vec4 A = texture2D(image, texCoord + vec2( -o.x,  o.y));
+    vec4 B = texture2D(image, texCoord + vec2(    0,  o.y));
+    vec4 C = texture2D(image, texCoord + vec2(  o.x,  o.y));
+    vec4 D = texture2D(image, texCoord + vec2( -o.x,    0));
+    vec4 E = texture2D(image, texCoord + vec2(    0,    0));
+    vec4 F = texture2D(image, texCoord + vec2(  o.x,    0));
+    vec4 G = texture2D(image, texCoord + vec2( -o.x, -o.y));
+    vec4 H = texture2D(image, texCoord + vec2(    0, -o.y));
+    vec4 I = texture2D(image, texCoord + vec2(  o.x, -o.y));
+    vec2 p = texCoord * textureDimensions;
+    // p = the position within a pixel [0...1]
+    vec4 R;
+    p = fract(p);
+    if (p.x > .5) {
+        if (p.y > .5) {
+            // Top Right
+            return B == F && B != D && F != H ? F : E;
+        } else {
+            // Bottom Right
+            return H == F && D != H && B != F ? F : E;
+        }
+    } else {
+        if (p.y > .5) {
+            // Top Left
+            return D == B && B != F && D != H ? D : E;
+        } else {
+            // Bottom Left
+            return D == H && D != B && H != F ? D : E;
+        }
+    }
+}
+
+vec4 filter(sampler2D image)
+{
+    // o = offset, the width of a pixel
+    vec2 o = 1.0 / (textureDimensions * 2.);
+    vec2 texCoord = vec2(gl_FragCoord.x, uResolution.y - gl_FragCoord.y) / uResolution;
+
+    // texel arrangement
+    // A B C
+    // D E F
+    // G H I
+    vec4 A = scale2x(image, texCoord + vec2( -o.x,  o.y));
+    vec4 B = scale2x(image, texCoord + vec2(    0,  o.y));
+    vec4 C = scale2x(image, texCoord + vec2(  o.x,  o.y));
+    vec4 D = scale2x(image, texCoord + vec2( -o.x,    0));
+    vec4 E = scale2x(image, texCoord + vec2(    0,    0));
+    vec4 F = scale2x(image, texCoord + vec2(  o.x,    0));
+    vec4 G = scale2x(image, texCoord + vec2( -o.x, -o.y));
+    vec4 H = scale2x(image, texCoord + vec2(    0, -o.y));
+    vec4 I = scale2x(image, texCoord + vec2(  o.x, -o.y));
+    vec2 p = texCoord * textureDimensions * 2.;
+    // p = the position within a pixel [0...1]
+    p = fract(p);
+    if (p.x > .5) {
+        if (p.y > .5) {
+            // Top Right
+            return B == F && B != D && F != H ? F : E;
+        } else {
+            // Bottom Right
+            return H == F && D != H && B != F ? F : E;
+        }
+    } else {
+        if (p.y > .5) {
+            // Top Left
+            return D == B && B != F && D != H ? D : E;
+        } else {
+            // Bottom Left
+            return D == H && D != B && H != F ? D : E;
+        }
+    }
+}

Shaders/SmoothBilinear.fsh

@@ -0,0 +1,18 @@
+vec4 filter(sampler2D image)
+{
+    vec2 texCoord = vec2(gl_FragCoord.x, uResolution.y - gl_FragCoord.y) / uResolution;
+
+    vec2 pixel = texCoord * textureDimensions;
+
+    vec4 q11 = texture2D(image, vec2(floor(pixel.x) / textureDimensions.x, floor(pixel.y) / textureDimensions.y));
+    vec4 q12 = texture2D(image, vec2(floor(pixel.x) / textureDimensions.x, ceil(pixel.y) / textureDimensions.y));
+    vec4 q21 = texture2D(image, vec2(ceil(pixel.x) / textureDimensions.x, floor(pixel.y) / textureDimensions.y));
+    vec4 q22 = texture2D(image, vec2(ceil(pixel.x) / textureDimensions.x, ceil(pixel.y) / textureDimensions.y));
+
+    vec2 smooth = smoothstep(0., 1., fract(pixel));
+
+    vec4 r1 = mix(q11, q21, fract(smooth.x));
+    vec4 r2 = mix(q12, q22, fract(smooth.x));
+
+    return mix (r1, r2, fract(smooth.y));
+}