[ProtonAOSP] blur: Calculate vertices in vertex shader instead of using VBO

Using a VBO for a simple full-screen triangle is unnecessarily
complicated, and because blur rendering is memory-bound, every little
bit of memory bandwidth counts. This removes the VBO in favor of
calculating the UV and clip space coordinates for a full-screen triangle
in the vertex shader, which only takes a few ALU instructions in a
shader that is only run 3 times per rendering step.

When tested with 2 layers of another 6-pass blur implementation, this
saves ~50 µs of rendering time on an Adreno 640 GPU at 1440x3040
resolution.

Change-Id: I6a3c6d691baa54412f4e04891129f101be6cdb60

2 files changed, 13 insertions, 57 deletions

diff --git a/libs/renderengine/gl/filters/BlurFilter.cpp b/libs/renderengine/gl/filters/BlurFilter.cpp
index d53fc8b25e..b139e4b3c5 100644
--- a/libs/renderengine/gl/filters/BlurFilter.cpp
+++ b/libs/renderengine/gl/filters/BlurFilter.cpp
@@ -41,15 +41,11 @@ BlurFilter::BlurFilter(GLESRenderEngine& engine)
         mDitherMixProgram(engine),
         mBlurProgram(engine) {
     mMixProgram.compile(getMixVertShader(), getMixFragShader());
-    mMPosLoc = mMixProgram.getAttributeLocation("aPosition");
-    mMUvLoc = mMixProgram.getAttributeLocation("aUV");
     mMBlurTextureLoc = mMixProgram.getUniformLocation("uBlurTexture");
     mMCompositionTextureLoc = mMixProgram.getUniformLocation("uCompositionTexture");
     mMBlurOpacityLoc = mMixProgram.getUniformLocation("uBlurOpacity");
 
     mDitherMixProgram.compile(getDitherMixVertShader(), getDitherMixFragShader());
-    mDPosLoc = mDitherMixProgram.getAttributeLocation("aPosition");
-    mDUvLoc = mDitherMixProgram.getAttributeLocation("aUV");
     mDNoiseUvScaleLoc = mDitherMixProgram.getUniformLocation("uNoiseUVScale");
     mDBlurTextureLoc = mDitherMixProgram.getUniformLocation("uBlurTexture");
     mDDitherTextureLoc = mDitherMixProgram.getUniformLocation("uDitherTexture");
@@ -60,8 +56,6 @@ BlurFilter::BlurFilter(GLESRenderEngine& engine)
                                GL_RGB8, GL_RGB, GL_UNSIGNED_BYTE);
 
     mBlurProgram.compile(getBlurVertShader(), getBlurFragShader());
-    mBPosLoc = mBlurProgram.getAttributeLocation("aPosition");
-    mBUvLoc = mBlurProgram.getAttributeLocation("aUV");
     mBTextureLoc = mBlurProgram.getUniformLocation("uTexture");
     mBOffsetLoc = mBlurProgram.getUniformLocation("uOffset");
 
@@ -76,20 +70,6 @@ BlurFilter::BlurFilter(GLESRenderEngine& engine)
     mBlurProgram.useProgram();
     glUniform1i(mBTextureLoc, 0);
     glUseProgram(0);
-
-    static constexpr auto size = 2.0f;
-    static constexpr auto translation = 1.0f;
-    const GLfloat vboData[] = {
-        // Vertex data
-        translation - size, -translation - size,
-        translation - size, -translation + size,
-        translation + size, -translation + size,
-        // UV data
-        0.0f, 0.0f - translation,
-        0.0f, size - translation,
-        size, size - translation
-    };
-    mMeshBuffer.allocateBuffers(vboData, 12 /* size */);
 }
 
 status_t BlurFilter::setAsDrawTarget(const DisplaySettings& display, uint32_t radius) {
@@ -146,17 +126,7 @@ status_t BlurFilter::setAsDrawTarget(const DisplaySettings& display, uint32_t ra
     return NO_ERROR;
 }
 
-void BlurFilter::drawMesh(GLuint uv, GLuint position) {
-
-    glEnableVertexAttribArray(uv);
-    glEnableVertexAttribArray(position);
-    mMeshBuffer.bind();
-    glVertexAttribPointer(position, 2 /* size */, GL_FLOAT, GL_FALSE,
-                          2 * sizeof(GLfloat) /* stride */, 0 /* offset */);
-    glVertexAttribPointer(uv, 2 /* size */, GL_FLOAT, GL_FALSE, 0 /* stride */,
-                          (GLvoid*)(6 * sizeof(GLfloat)) /* offset */);
-    mMeshBuffer.unbind();
-
+void BlurFilter::drawMesh() {
     // draw mesh
     glDrawArrays(GL_TRIANGLES, 0 /* first */, 3 /* count */);
 }
@@ -199,7 +169,7 @@ status_t BlurFilter::prepare() {
         glBindTexture(GL_TEXTURE_2D, read->getTextureName());
         glUniform2f(mBOffsetLoc, stepX * i, stepY * i);
 
-        drawMesh(mBUvLoc, mBPosLoc);
+        drawMesh();
 
         // Swap buffers for next iteration
         std::swap(read, draw);
@@ -234,11 +204,11 @@ status_t BlurFilter::render(size_t layers, int currentLayer) {
     if (currentLayer == layers - 1) {
         mDitherMixProgram.useProgram();
         glUniform1f(mDBlurOpacityLoc, opacity);
-        drawMesh(mDUvLoc, mDPosLoc);
+        drawMesh();
     } else {
         mMixProgram.useProgram();
         glUniform1f(mMBlurOpacityLoc, opacity);
-        drawMesh(mMUvLoc, mMPosLoc);
+        drawMesh();
     }
 
     glUseProgram(0);
@@ -253,14 +223,12 @@ string BlurFilter::getBlurVertShader() const {
 
         uniform vec2 uOffset;
 
-        in vec2 aPosition;
-        in vec2 aUV;
         out vec2 vUV;
         out vec2 vBlurTaps[4];
 
         void main() {
-            vUV = aUV;
-            gl_Position = vec4(aPosition, 0.0, 1.0);
+            vUV = vec2((gl_VertexID == 2) ? 2.0 : 0.0, (gl_VertexID == 1) ? 2.0 : 0.0);
+            gl_Position = vec4(vUV * 2.0 - 1.0, 1.0, 1.0);
 
             vBlurTaps[0] = vUV + vec2( uOffset.x,  uOffset.y);
             vBlurTaps[1] = vUV + vec2( uOffset.x, -uOffset.y);
@@ -296,13 +264,11 @@ string BlurFilter::getMixVertShader() const {
     return R"SHADER(#version 310 es
         precision mediump float;
 
-        in vec2 aPosition;
-        in vec2 aUV;
         out vec2 vUV;
 
         void main() {
-            vUV = aUV;
-            gl_Position = vec4(aPosition, 0.0, 1.0);
+            vUV = vec2((gl_VertexID == 2) ? 2.0 : 0.0, (gl_VertexID == 1) ? 2.0 : 0.0);
+            gl_Position = vec4(vUV * 2.0 - 1.0, 1.0, 1.0);
         }
     )SHADER";
 }
@@ -333,15 +299,14 @@ string BlurFilter::getDitherMixVertShader() const {
 
         uniform vec2 uNoiseUVScale;
 
-        in vec2 aPosition;
-        in vec2 aUV;
         out vec2 vUV;
         out vec2 vNoiseUV;
 
         void main() {
-            vUV = aUV;
-            vNoiseUV = aUV * uNoiseUVScale;
-            gl_Position = vec4(aPosition, 0.0, 1.0);
+            vUV = vec2((gl_VertexID == 2) ? 2.0 : 0.0, (gl_VertexID == 1) ? 2.0 : 0.0);
+            gl_Position = vec4(vUV * 2.0 - 1.0, 1.0, 1.0);
+
+            vNoiseUV = vUV * uNoiseUVScale;
         }
     )SHADER";
 }
diff --git a/libs/renderengine/gl/filters/BlurFilter.h b/libs/renderengine/gl/filters/BlurFilter.h
index e5dae7b9ea..df2ca1deca 100644
--- a/libs/renderengine/gl/filters/BlurFilter.h
+++ b/libs/renderengine/gl/filters/BlurFilter.h
@@ -53,7 +53,7 @@ public:
 
 private:
     uint32_t mRadius;
-    void drawMesh(GLuint uv, GLuint position);
+    void drawMesh();
     string getBlurVertShader() const;
     string getBlurFragShader() const;
     string getMixVertShader() const;
@@ -76,19 +76,12 @@ private:
     // Buffer holding the final blur pass.
     GLFramebuffer* mLastDrawTarget;
 
-    // VBO containing vertex and uv data of a fullscreen triangle.
-    GLVertexBuffer mMeshBuffer;
-
     GenericProgram mMixProgram;
-    GLuint mMPosLoc;
-    GLuint mMUvLoc;
     GLuint mMBlurOpacityLoc;
     GLuint mMBlurTextureLoc;
     GLuint mMCompositionTextureLoc;
 
     GenericProgram mDitherMixProgram;
-    GLuint mDPosLoc;
-    GLuint mDUvLoc;
     GLuint mDNoiseUvScaleLoc;
     GLuint mDBlurOpacityLoc;
     GLuint mDBlurTextureLoc;
@@ -96,8 +89,6 @@ private:
     GLuint mDCompositionTextureLoc;
 
     GenericProgram mBlurProgram;
-    GLuint mBPosLoc;
-    GLuint mBUvLoc;
     GLuint mBTextureLoc;
     GLuint mBOffsetLoc;
 };