I didn't see anything in this message that suggested "we should drop everything
we're doing and start on this right now", but most of the early comments I'm
seeing are commenting on that. Let's make that a separate discussion.
If we didn't have all these variations, what would we do? Would we just do
one, then add more (and add code complexity) only if we find significant
performance improvements? I'd have to go with "probably yes" on that one :)
Let's see if we can focus the discussion on "what should we have", and then on
"how do we get there", and let's not worry about when and how for now. Gets in
the way.
--
- Milan
On 2013-10-10, at 7:59 , Andreas Gal <andreas....@gmail.com> wrote:
> Hi,
>
> we currently have a zoo of shaders to render layers:
>
> RGBALayerProgramType,
> BGRALayerProgramType,
> RGBXLayerProgramType,
> BGRXLayerProgramType,
> RGBARectLayerProgramType,
> RGBXRectLayerProgramType,
> BGRARectLayerProgramType,
> RGBAExternalLayerProgramType,
> ColorLayerProgramType,
> YCbCrLayerProgramType,
> ComponentAlphaPass1ProgramType,
> ComponentAlphaPass1RGBProgramType,
> ComponentAlphaPass2ProgramType,
> ComponentAlphaPass2RGBProgramType,
>
> (I have just eliminated the Copy2D variants, so omitted here.)
>
> Next, I would like to replace everything but the YCbCr and ComponentAlpha
> shaders with one unified shader (attached below).
>
> Rationale:
>
> Most of our shader programs only differ minimally in cycle count, and we are
> generally memory bound, not GPU cycle bound (even on mobile). In addition,
> GPUs are actually are very efficient at branching, as long the branch is
> uniform and doesn't change direction per pixel or vertex (the driver compiles
> essentially variants and runs that). Last but not least, switching shaders
> tends to be expensive.
>
> Proposed approach:
>
> We use a single shader to replace the current 8 layer shaders. I verified
> with the mali shader compiler that the shortest path (color layer) is pretty
> close to the old color shader (is now 3, due to the opacity multiplication,
> was 1). For a lot of scenes we will be able to render without ever switching
> shaders, so that should more than make up for the extra cycles, especially
> since we are memory bound anyway.
>
> More uniforms have to be set per shader invocation, but that should be pretty
> cheap.
>
> I completely dropped the distinction of 2D and 3D masks. 3D masks should be
> able to handle the 2D case and the cycle savings are minimal, and as
> mentioned before, irrelevant.
>
> An important advantage is that with this approach we can now easily add
> additional layer effects to the pipeline without exponentially exploding the
> number of programs
> (RGBXRectLayerProgramWithGrayscaleAndWithoutOpacityButMaskAndNotMask3D…).
>
> Also, last but not least, this reduces code complexity quite a bit.
>
> Feedback welcome.
>
> Thanks,
>
> Andreas
>
> ---
>
> // Base color (will be rendered if layer texture is not read).
> uniform vec4 uColor;
>
> // Layer texture (disabled for color layers).
> uniform bool uTextureEnabled;
> uniform vec2 uTexCoordMultiplier;
> uniform bool uTextureBGRA; // Default is RGBA.
> uniform bool uTextureNoAlpha;
> uniform float uTextureOpacity;
> uniform sampler2D uTexture;
> uniform bool uTextureUseExternalOES;
> uniform samplerExternalOES uTextureExternalOES;
> #ifndef GL_ES
> uniform bool uTextureUseRect;
> uniform sampler2DRect uTextureRect;
> #endif
>
> // Masking (optional)
> uniform bool uMaskEnabled;
> varying vec3 vMaskCoord;
> uniform sampler2D uMaskTexture;
>
> void main()
> {
> vec4 color = uColor;
> if (uTextureEnabled) {
> vec2 texCoord = vTexCoord * uTexCoordMultiplier;
> if (uTextureUseExternalOES) {
> color = texture2D(uTextureExternalOES, texCoord);
> #ifndef GL_ES
> } else if (uTextureUseRect) {
> color = texture2DRect(uTexture, texCoord);
> #endif
> } else {
> color = texture2D(uTexture, texCoord);
> }
> if (uTextureBGRA) {
> color = color.bgra;
> }
> if (uTextureNoAlpha) {
> color = vec4(color.rgb, 1.0);
> }
> color *= uTextureOpacity;
> }
> if (uMaskEnabled) {
> color *= texture2D(uMaskTexture, vMaskCoord.xy / vMaskCoord.z).r;
> }
> gl_FragColor = color;
> }
>
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