Make gradients beautiful again

Bug #7239634

This change passes two matrices to the vertex shader instead of one.
We used to compute the final MVP matrix on the CPU to minimize the
number of operations in the vertex shaders. Shader compilers are
however smart enough to perform this optimization for us. Since we
need the MV matrix to properly compute gradients dithering, this
change splits the MVP matrix into two. This has the advantage of
removing one matrix multiplication per drawing operation on the
CPU.
The SGX 540 shader compiler produces the same number of instructions
in both cases. There is no penalty hit with having two matrices
instead of one. We also send so few vertices per frame that it
does not matter very much.

Change-Id: I17d47ac4772615418e0e1885b97493d31435a936

1 files changed, 6 insertions, 3 deletions

diff --git a/libs/hwui/Program.cpp b/libs/hwui/Program.cpp
index 5b1b57d3a664..f0b5553a79a7 100644
--- a/libs/hwui/Program.cpp
+++ b/libs/hwui/Program.cpp
@@ -81,6 +81,7 @@ Program::Program(const ProgramDescription& description, const char* vertex, cons
 
     if (mInitialized) {
         transform = addUniform("transform");
+        projection = addUniform("projection");
     }
 }
 
@@ -152,18 +153,20 @@ GLuint Program::buildShader(const char* source, GLenum type) {
 
 void Program::set(const mat4& projectionMatrix, const mat4& modelViewMatrix,
         const mat4& transformMatrix, bool offset) {
-    mat4 t(projectionMatrix);
+    mat4 p(projectionMatrix);
     if (offset) {
         // offset screenspace xy by an amount that compensates for typical precision
         // issues in GPU hardware that tends to paint hor/vert lines in pixels shifted
         // up and to the left.
         // This offset value is based on an assumption that some hardware may use as
         // little as 12.4 precision, so we offset by slightly more than 1/16.
-        t.translate(.375, .375, 0);
+        p.translate(.375, .375, 0);
     }
-    t.multiply(transformMatrix);
+
+    mat4 t(transformMatrix);
     t.multiply(modelViewMatrix);
 
+    glUniformMatrix4fv(projection, 1, GL_FALSE, &p.data[0]);
     glUniformMatrix4fv(transform, 1, GL_FALSE, &t.data[0]);
 }