Always apply UniformMatrix4fvStreamTextureMatrixCHROMIUM matrix argument.

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index f28cc4387e7832e07bdf8335f303ff646fd0293c..e4728293d3aaac1b8f9e96ac3a787925771f141c 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -7617,16 +7617,9 @@ void GLES2DecoderImpl::DoUniformMatrix4fv(
 void GLES2DecoderImpl::DoUniformMatrix4fvStreamTextureMatrixCHROMIUM(
     GLint fake_location,
     GLboolean transpose,
-    const GLfloat* default_value) {
+    const GLfloat* transform) {
   float gl_matrix[16];
 
-  // If we can't get a matrix from the texture, then use a default.
-  // TODO(liberato): remove |default_value| and replace with an identity matrix.
-  // It is only present as a transitionary step until StreamTexture supplies
-  // the matrix via GLImage.  Once that happens, GLRenderer can quit sending
-  // in a default.
-  memcpy(gl_matrix, default_value, sizeof(gl_matrix));
-
   // This refers to the bound external texture on the active unit.
   TextureUnit& unit = state_.texture_units[state_.active_texture_unit];
   if (TextureRef* texture_ref = unit.bound_texture_external_oes.get()) {
@@ -7634,6 +7627,19 @@ void GLES2DecoderImpl::DoUniformMatrix4fvStreamTextureMatrixCHROMIUM(
             texture_ref->texture()->GetLevelStreamTextureImage(
                 GL_TEXTURE_EXTERNAL_OES, 0)) {
       image->GetTextureMatrix(gl_matrix);

[liberato (no reviews please), 2016/03/31 15:03:16]

maybe not for this CL, but GetFlippedTextureMatrix might not be the best name in
retrospect.  GetChromiumTextureMatrix or similar, since nobody will care what
changes are made to the original, only that it's now in chromium coordinates.

or, just GetTextureMatrix.  i think that was your original proposal, and i agree
that you were right.  :)

[liberato (no reviews please), 2016/03/31 15:03:16]

don't we want this to be GetFlippedTextureMatrix?  that lets the shader be more
intuitive.

[Tobias Sargeant, 2016/04/01 11:59:10]

Done. On reflection I decided against GetChromiumTextureMatrix in favour of
requiring GetTextureMatrix to return a matrix that converts chromium orientation
texel coordinates into whatever coordinates are appropriate for whatever
GLStreamTextureImage wraps. For ADVA and StreamTextureAndroid this involves a
y-flip, so I made both use a convenience function for that explicitly.

[liberato (no reviews please), 2016/04/01 14:07:13]

makes sense.

+      GLfloat tmp[16];

[liberato (no reviews please), 2016/03/31 15:03:16]

without this premultiply, does the y-flip without UMP come back?  if so, then it
raises the question why !UMP is sending down a y-flip.

i don't see what else in this CL could change the behavior, but i also don't see
why it would affect !UMP only.

+      for (int c = 0; c < 16; c += 4) {
+        for (int r = 0; r < 4; ++r) {
+          tmp[c + r] = 0.0f;
+          for (int i = 0; i < 4; ++i) {
+            tmp[c + r] += gl_matrix[r + 4 * i] * transform[c + i];
+          }
+        }
+      }
+      std::copy(tmp, tmp + 16, gl_matrix);
+    } else {
+      // Missing stream texture. Treat matrix as identity.
+      memcpy(gl_matrix, transform, sizeof(gl_matrix));
     }
   } else {
     LOCAL_SET_GL_ERROR(GL_INVALID_OPERATION,