Clamp YUV videos to their visible size in the shader

cc/output/shader.cc

Index: cc/output/shader.cc
diff --git a/cc/output/shader.cc b/cc/output/shader.cc
index 5bc704497ca5b63c24547ac5d9ea15092783b454..ad0a939d458f7f303529c234496eb4a18d63de3e 100644
--- a/cc/output/shader.cc
+++ b/cc/output/shader.cc
@@ -191,14 +191,17 @@ std::string VertexShaderPosTex::GetShaderString() const {
 }
 
 VertexShaderPosTexYUVStretchOffset::VertexShaderPosTexYUVStretchOffset()
-    : matrix_location_(-1), tex_scale_location_(-1), tex_offset_location_(-1) {
+    : matrix_location_(-1),
+      tex_scale_location_(-1),
+      tex_offset_location_(-1),
+      clamp_size_location_(-1) {
 }
 
 void VertexShaderPosTexYUVStretchOffset::Init(GLES2Interface* context,
                                               unsigned program,
                                               int* base_uniform_index) {
   static const char* uniforms[] = {
-      "matrix", "texScale", "texOffset",
+      "matrix", "texScale", "texOffset", "clampSize",
   };
   int locations[arraysize(uniforms)];
 
@@ -211,22 +214,21 @@ void VertexShaderPosTexYUVStretchOffset::Init(GLES2Interface* context,
   matrix_location_ = locations[0];
   tex_scale_location_ = locations[1];
   tex_offset_location_ = locations[2];
+  clamp_size_location_ = locations[3];
 }
 
 std::string VertexShaderPosTexYUVStretchOffset::GetShaderString() const {
   // clang-format off
   return VERTEX_SHADER(
       // clang-format on
-      precision mediump float;
-      attribute vec4 a_position;
-      attribute TexCoordPrecision vec2 a_texCoord;
-      uniform mat4 matrix;
+      precision mediump float; attribute vec4 a_position;
+      attribute TexCoordPrecision vec2 a_texCoord; uniform mat4 matrix;
       varying TexCoordPrecision vec2 v_texCoord;
       uniform TexCoordPrecision vec2 texScale;
       uniform TexCoordPrecision vec2 texOffset;
-      void main() {
+      uniform TexCoordPrecision vec2 clampSize; void main() {

[danakj, 2015/01/28 01:02:00]

formatting..

[enne (OOO), 2015/01/31 01:32:13]

git cl format T_T

         gl_Position = matrix * a_position;
-        v_texCoord = a_texCoord * texScale + texOffset;
+        v_texCoord = min(clampSize, a_texCoord * texScale + texOffset);

[danakj, 2015/01/28 01:02:00]

do we not have to clamp on the left/top too?

[enne (OOO), 2015/01/31 01:32:13]

Turns out we do.  Thanks.  I changed clampSize to clampRect in the shader, but
left it as "texture size" in the quad, since that's easier to specify.

       }
       // clang-format off
   );  // NOLINT(whitespace/parens)