A couple of MAD optimizations, some formatting and ensure the shader

works a little bit better.
If the blending_mode macro on gb-pass1 is set to 0, we'll get only the
green background color.

handheld/gameboy/shader-files/gb-pass0.slang

@@ -59,7 +59,7 @@ layout(location = 3) out vec2 one_texel;
 
 
 // Largest integer scale of input video that will fit in the current output (y axis would typically be limiting on widescreens)
-#define video_scale         floor(global.OutputSize.y / global.SourceSize.y)        
+#define video_scale         floor(global.OutputSize.y * global.SourceSize.w)        
 
 // Size of the scaled video
 #define scaled_video_out    (global.SourceSize.xy * vec2(video_scale))       
@@ -130,7 +130,8 @@ void main()
     input_rgb += (prev5_rgb - input_rgb) * pow(response_time, 6.0);
     input_rgb += (prev6_rgb - input_rgb) * pow(response_time, 7.0);
 
-    float rgb_to_alpha = (input_rgb.r + input_rgb.g + input_rgb.b) / 3.0 + (is_on_dot * baseline_alpha);
+    float rgb_to_alpha = (input_rgb.r + input_rgb.g + input_rgb.b) * 0.333333333
+                        + (is_on_dot * baseline_alpha);
 
     // Apply foreground color and assign alpha value
     // Apply the foreground color to all texels -

handheld/gameboy/shader-files/gb-pass1.slang

@@ -14,7 +14,8 @@ layout(std140, set = 0, binding = 0) uniform UBO
 
 // 0 - only the space between dots is blending
 // 1 - all texels are blended
-#define blending_mode 0             
+/* TODO/FIXME - When set to zero, frame will be a solid green color */
+#define blending_mode 1             
 
 // The amount of alpha swapped between neighboring texels
 #define adjacent_texel_alpha_blending 0.1755  

handheld/gameboy/shader-files/gb-pass3.slang

@@ -98,16 +98,16 @@ void main()
                                 0.10164546793794160274995705611009,      
                                 0.08167444001912718529866079800870 );
 
-    //sample the current fragment and apply its weight
+    // Sample the current fragment and apply its weight
     vec4 out_color = texture(Source, clamp(vTexCoord, lower_bound, upper_bound)) * weights[0];
 
-    //iterate across the offsets in both directions sampling texels and adding their weighted alpha values to the total
+    // Iterate across the offsets in both directions sampling texels
+    // and adding their weighted alpha values to the total
     for (int i = 1; i < 5; i++)
     {
         out_color.a += texture(Source, clamp(vTexCoord + vec2(0.0, offsets[i] * texel.y), lower_bound, upper_bound)).a * weights[i];
         out_color.a += texture(Source, clamp(vTexCoord - vec2(0.0, offsets[i] * texel.y), lower_bound, upper_bound)).a * weights[i];
     }
 
-    //return the new value
-    FragColor = vec4(out_color.rgb, 1.0);
+    FragColor = out_color;
 }