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..21361482edaba57b042089e334a65a055db14116 100644
--- a/cc/output/shader.cc
+++ b/cc/output/shader.cc
@@ -191,7 +191,9 @@ 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) {
 }
 
 void VertexShaderPosTexYUVStretchOffset::Init(GLES2Interface* context,
@@ -217,8 +219,7 @@ std::string VertexShaderPosTexYUVStretchOffset::GetShaderString() const {
   // clang-format off
   return VERTEX_SHADER(
       // clang-format on
-      precision mediump float;
-      attribute vec4 a_position;
+      precision mediump float; attribute vec4 a_position;

[danakj, 2015/02/02 18:43:03]

?

       attribute TexCoordPrecision vec2 a_texCoord;
       uniform mat4 matrix;
       varying TexCoordPrecision vec2 v_texCoord;
@@ -1741,15 +1742,20 @@ FragmentShaderYUVVideo::FragmentShaderYUVVideo()
       v_texture_location_(-1),
       alpha_location_(-1),
       yuv_matrix_location_(-1),
-      yuv_adj_location_(-1) {
+      yuv_adj_location_(-1),
+      clamp_rect_location_(-1) {
 }
 
 void FragmentShaderYUVVideo::Init(GLES2Interface* context,
                                   unsigned program,
                                   int* base_uniform_index) {
-  static const char* uniforms[] = {
-      "y_texture", "u_texture", "v_texture", "alpha", "yuv_matrix", "yuv_adj",
-  };
+  static const char* uniforms[] = {"y_texture",
+                                   "u_texture",
+                                   "v_texture",
+                                   "alpha",
+                                   "yuv_matrix",
+                                   "yuv_adj",
+                                   "clamp_rect"};
   int locations[arraysize(uniforms)];
 
   GetProgramUniformLocations(context,
@@ -1764,6 +1770,7 @@ void FragmentShaderYUVVideo::Init(GLES2Interface* context,
   alpha_location_ = locations[3];
   yuv_matrix_location_ = locations[4];
   yuv_adj_location_ = locations[5];
+  clamp_rect_location_ = locations[6];
 }
 
 std::string FragmentShaderYUVVideo::GetShaderString(TexCoordPrecision precision,
@@ -1780,10 +1787,12 @@ std::string FragmentShaderYUVVideo::GetShaderString(TexCoordPrecision precision,
       uniform float alpha;
       uniform vec3 yuv_adj;
       uniform mat3 yuv_matrix;
+      uniform vec4 clamp_rect;
       void main() {
-        float y_raw = TextureLookup(y_texture, v_texCoord).x;
-        float u_unsigned = TextureLookup(u_texture, v_texCoord).x;
-        float v_unsigned = TextureLookup(v_texture, v_texCoord).x;
+        vec2 clamped = max(clamp_rect.xy, min(clamp_rect.zw, v_texCoord));

[enne (OOO), 2015/01/31 01:32:14]

I moved the clamping from the vertex to the fragment shader, because otherwise
it would cause stretching of the texture, rather than just more localized
clamping.

+        float y_raw = TextureLookup(y_texture, clamped).x;
+        float u_unsigned = TextureLookup(u_texture, clamped).x;
+        float v_unsigned = TextureLookup(v_texture, clamped).x;
         vec3 yuv = vec3(y_raw, u_unsigned, v_unsigned) + yuv_adj;
         vec3 rgb = yuv_matrix * yuv;
         gl_FragColor = vec4(rgb, 1.0) * alpha;
@@ -1814,6 +1823,7 @@ void FragmentShaderYUVAVideo::Init(GLES2Interface* context,
       "alpha",
       "cc_matrix",
       "yuv_adj",
+      "clamp_rect",
   };
   int locations[arraysize(uniforms)];
 
@@ -1830,6 +1840,7 @@ void FragmentShaderYUVAVideo::Init(GLES2Interface* context,
   alpha_location_ = locations[4];
   yuv_matrix_location_ = locations[5];
   yuv_adj_location_ = locations[6];
+  clamp_rect_location_ = locations[7];
 }
 
 std::string FragmentShaderYUVAVideo::GetShaderString(
@@ -1848,11 +1859,13 @@ std::string FragmentShaderYUVAVideo::GetShaderString(
       uniform float alpha;
       uniform vec3 yuv_adj;
       uniform mat3 yuv_matrix;
+      uniform vec4 clamp_rect;
       void main() {
-        float y_raw = TextureLookup(y_texture, v_texCoord).x;
-        float u_unsigned = TextureLookup(u_texture, v_texCoord).x;
-        float v_unsigned = TextureLookup(v_texture, v_texCoord).x;
-        float a_raw = TextureLookup(a_texture, v_texCoord).x;
+        vec2 clamped = max(clamp_rect.xy, min(clamp_rect.zw, v_texCoord));
+        float y_raw = TextureLookup(y_texture, clamped).x;
+        float u_unsigned = TextureLookup(u_texture, clamped).x;
+        float v_unsigned = TextureLookup(v_texture, clamped).x;
+        float a_raw = TextureLookup(a_texture, clamped).x;
         vec3 yuv = vec3(y_raw, u_unsigned, v_unsigned) + yuv_adj;
         vec3 rgb = yuv_matrix * yuv;
         gl_FragColor = vec4(rgb, 1.0) * (alpha * a_raw);