rhi: gl: Best uniform is no uniform

Artificial tests with tens of thousands of meshes drawn with
the same program (graphics pipeline) and almost the same
uniform values (the difference being in the normal and model
and view matrices) do benefit - strongly depending on the GL
implementation probably - from doing fewer glUniformNf[v] calls.

Building on the fact that uniform location values will typically
be an int value starting at 0 (not guaranteed of course, we just
skip the smartness in that case), we can dedicate a small 16K
block to keep track of float/vec3/vec3/vec4 values in the graphics
and compute pipeline objects.

Change-Id: I217c31ccdeb511b3e8b8286078d7fbde399c8e3b
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

1 files changed, 9 insertions, 0 deletions

diff --git a/src/gui/rhi/qrhigles2_p_p.h b/src/gui/rhi/qrhigles2_p_p.h
index 95bf85f0b4..07e0466b30 100644
--- a/src/gui/rhi/qrhigles2_p_p.h
+++ b/src/gui/rhi/qrhigles2_p_p.h
@@ -269,6 +269,13 @@ Q_DECLARE_TYPEINFO(QGles2SamplerDescription, Q_MOVABLE_TYPE);
 using QGles2UniformDescriptionVector = QVarLengthArray<QGles2UniformDescription, 8>;
 using QGles2SamplerDescriptionVector = QVarLengthArray<QGles2SamplerDescription, 4>;
 
+struct QGles2UniformState
+{
+    static constexpr int MAX_TRACKED_LOCATION = 1023;
+    int componentCount;
+    float v[4];
+};
+
 struct QGles2GraphicsPipeline : public QRhiGraphicsPipeline
 {
     QGles2GraphicsPipeline(QRhiImplementation *rhi);
@@ -280,6 +287,7 @@ struct QGles2GraphicsPipeline : public QRhiGraphicsPipeline
     GLenum drawMode = GL_TRIANGLES;
     QGles2UniformDescriptionVector uniforms;
     QGles2SamplerDescriptionVector samplers;
+    QGles2UniformState uniformState[QGles2UniformState::MAX_TRACKED_LOCATION + 1];
     uint generation = 0;
     friend class QRhiGles2;
 };
@@ -294,6 +302,7 @@ struct QGles2ComputePipeline : public QRhiComputePipeline
     GLuint program = 0;
     QGles2UniformDescriptionVector uniforms;
     QGles2SamplerDescriptionVector samplers;
+    QGles2UniformState uniformState[QGles2UniformState::MAX_TRACKED_LOCATION + 1];
     uint generation = 0;
     friend class QRhiGles2;
 };