Add simple DMG shader

Cocoa/GBPreferencesWindow.m

@@ -29,6 +29,7 @@
                     @"Bilinear",
                     @"SmoothBilinear",
                     @"LCD",
+                    @"DMG",
                     @"Scale2x",
                     @"Scale4x",
                     @"AAScale2x",

SDL/gui.c

@@ -357,6 +357,7 @@ struct shader_name {
     {"Bilinear", "Bilinear"},
     {"SmoothBilinear", "Smooth Bilinear"},
     {"LCD", "LCD Display"},
+    {"DMG", "DMG Display"},
     {"Scale2x", "Scale2x"},
     {"Scale4x", "Scale4x"},
     {"AAScale2x", "Anti-aliased Scale2x"},

Shaders/DMG.fsh

@@ -0,0 +1,38 @@
+vec4 pixelize(vec4 image, vec2 scaleVec, vec2 texCoord) {
+	float scale = max(scaleVec.x, scaleVec.y);
+	float x = fract(texCoord.x * 160.0) * scale;
+	float y = fract(texCoord.y * 144.0) * scale;
+
+	float border = 1.0;
+
+	if (scale > 5.0) {
+		border = 2.0;
+	}
+
+	if (x < border || x > scale - border || y < border || y > scale - border) {
+		return vec4(.95, .95, .95, 1);
+	}
+
+	return image;
+}
+
+vec4 scale(sampler2D image) {
+	vec2 displayScale = uResolution / vec2(160.0, 144.0);
+	vec2 texCoord = vec2(gl_FragCoord.x, uResolution.y - gl_FragCoord.y) / uResolution;
+	vec4 sampled = texture(image, texCoord);
+
+	if (displayScale.x < 3.0 || displayScale.y < 3.0) {
+		return sampled;
+	}
+
+	float mixValue = 1.0;
+
+	if (displayScale.x >= 5.0 && displayScale.y >= 5.0) {
+		mixValue = 0.5;
+	}
+	else if (displayScale.x >= 3.0 && displayScale.y >= 3.0) {
+		mixValue = 0.8;
+	}
+
+	return mix(pixelize(sampled, displayScale, texCoord), sampled, mixValue);
+}