Shaders: assume drawOffset is 0 if DRAW_COUNT is 1.

This is always true in the single-draw case, since setDrawOffset()
asserts on this. In the multi-draw case this optimization doesn't make
sense, because it doesn't make sense to create a multidraw shader with
just one draw.

On an Intel 630 GPU this resulted in single-draw single-material Phong
to go from 550 ms to 440, which is roughly a 20% improvement. For the
simpler shaders the difference is even higher. The multidraw numbers
stayed the same as before, obviously.

src/Magnum/Shaders/DistanceFieldVector.frag

@@ -72,6 +72,7 @@ uniform lowp float smoothness
 
 #else
 #ifndef MULTI_DRAW
+#if DRAW_COUNT > 1
 #ifdef EXPLICIT_UNIFORM_LOCATION
 layout(location = 0)
 #endif
@@ -80,6 +81,9 @@ uniform highp uint drawOffset
     = 0u
     #endif
     ;
+#else
+#define drawOffset 0u
+#endif
 #define drawId drawOffset
 #endif
 

src/Magnum/Shaders/DistanceFieldVectorGL.cpp

@@ -165,7 +165,7 @@ template<UnsignedInt dimensions> DistanceFieldVectorGL<dimensions>::DistanceFiel
     {
         #ifndef MAGNUM_TARGET_GLES2
         if(flags >= Flag::UniformBuffers) {
-            _drawOffsetUniform = uniformLocation("drawOffset");
+            if(_drawCount > 1) _drawOffsetUniform = uniformLocation("drawOffset");
         } else
         #endif
         {
@@ -280,7 +280,7 @@ template<UnsignedInt dimensions> DistanceFieldVectorGL<dimensions>& DistanceFiel
         "Shaders::DistanceFieldVectorGL::setDrawOffset(): the shader was not created with uniform buffers enabled", *this);
     CORRADE_ASSERT(offset < _drawCount,
         "Shaders::DistanceFieldVectorGL::setDrawOffset(): draw offset" << offset << "is out of bounds for" << _drawCount << "draws", *this);
-    setUniform(_drawOffsetUniform, offset);
+    if(_drawCount > 1) setUniform(_drawOffsetUniform, offset);
     return *this;
 }
 

src/Magnum/Shaders/DistanceFieldVectorGL.h

@@ -445,7 +445,9 @@ template<UnsignedInt dimensions> class MAGNUM_SHADERS_EXPORT DistanceFieldVector
          * @ref bindTransformationProjectionBuffer(), @ref bindDrawBuffer() and
          * @ref bindTextureTransformationBuffer() should be used for current
          * draw. Expects that @ref Flag::UniformBuffers is set and @p offset is
-         * less than @ref drawCount(). Initial value is @cpp 0 @ce.
+         * less than @ref drawCount(). Initial value is @cpp 0 @ce, if
+         * @ref drawCount() is @cpp 1 @ce, the function is a no-op as the
+         * shader assumes draw offset to be always zero.
          *
          * If @ref Flag::MultiDraw is set, @glsl gl_DrawID @ce is added to this
          * value, which makes each draw submitted via

src/Magnum/Shaders/Flat.frag

@@ -72,6 +72,7 @@ uniform highp uint objectId; /* defaults to zero */
 
 #else
 #ifndef MULTI_DRAW
+#if DRAW_COUNT > 1
 #ifdef EXPLICIT_UNIFORM_LOCATION
 layout(location = 0)
 #endif
@@ -80,6 +81,9 @@ uniform highp uint drawOffset
     = 0u
     #endif
     ;
+#else
+#define drawOffset 0u
+#endif
 #define drawId drawOffset
 #endif
 

src/Magnum/Shaders/Flat.vert

@@ -92,6 +92,7 @@ uniform highp uint textureLayer; /* defaults to zero */
 /* Uniform buffers */
 
 #else
+#if DRAW_COUNT > 1
 #ifdef EXPLICIT_UNIFORM_LOCATION
 layout(location = 0)
 #endif
@@ -100,6 +101,9 @@ uniform highp uint drawOffset
     = 0u
     #endif
     ;
+#else
+#define drawOffset 0u
+#endif
 
 layout(std140
     #ifdef EXPLICIT_BINDING

src/Magnum/Shaders/FlatGL.cpp

@@ -216,7 +216,7 @@ template<UnsignedInt dimensions> FlatGL<dimensions>::FlatGL(const Flags flags
     {
         #ifndef MAGNUM_TARGET_GLES2
         if(flags >= Flag::UniformBuffers) {
-            _drawOffsetUniform = uniformLocation("drawOffset");
+            if(_drawCount > 1) _drawOffsetUniform = uniformLocation("drawOffset");
         } else
         #endif
         {
@@ -342,7 +342,7 @@ template<UnsignedInt dimensions> FlatGL<dimensions>& FlatGL<dimensions>::setDraw
         "Shaders::FlatGL::setDrawOffset(): the shader was not created with uniform buffers enabled", *this);
     CORRADE_ASSERT(offset < _drawCount,
         "Shaders::FlatGL::setDrawOffset(): draw offset" << offset << "is out of bounds for" << _drawCount << "draws", *this);
-    setUniform(_drawOffsetUniform, offset);
+    if(_drawCount > 1) setUniform(_drawOffsetUniform, offset);
     return *this;
 }
 

src/Magnum/Shaders/FlatGL.h

@@ -755,7 +755,9 @@ template<UnsignedInt dimensions> class MAGNUM_SHADERS_EXPORT FlatGL: public GL::
          * @ref bindTransformationProjectionBuffer(), @ref bindDrawBuffer() and
          * @ref bindTextureTransformationBuffer() should be used for current
          * draw. Expects that @ref Flag::UniformBuffers is set and @p offset is
-         * less than @ref drawCount(). Initial value is @cpp 0 @ce.
+         * less than @ref drawCount(). Initial value is @cpp 0 @ce, if
+         * @ref drawCount() is @cpp 1 @ce, the function is a no-op as the
+         * shader assumes draw offset to be always zero.
          *
          * If @ref Flag::MultiDraw is set, @glsl gl_DrawID @ce is added to this
          * value, which makes each draw submitted via

src/Magnum/Shaders/MeshVisualizer.frag

@@ -111,6 +111,7 @@ uniform lowp vec2 colorMapOffsetScale
 
 #else
 #ifndef MULTI_DRAW
+#if DRAW_COUNT > 1
 #ifdef EXPLICIT_UNIFORM_LOCATION
 layout(location = 1)
 #endif
@@ -119,6 +120,9 @@ uniform highp uint drawOffset
     = 0u
     #endif
     ;
+#else
+#define drawOffset 0u
+#endif
 #define drawId drawOffset
 #endif
 

src/Magnum/Shaders/MeshVisualizer.vert

@@ -113,6 +113,7 @@ uniform highp float lineLength
 /* Uniform buffers */
 
 #else
+#if DRAW_COUNT > 1
 #ifdef EXPLICIT_UNIFORM_LOCATION
 layout(location = 1)
 #endif
@@ -121,6 +122,9 @@ uniform highp uint drawOffset
     = 0u
     #endif
     ;
+#else
+#define drawOffset 0u
+#endif
 
 #ifdef TWO_DIMENSIONS
 layout(std140

src/Magnum/Shaders/MeshVisualizerGL.cpp

@@ -263,7 +263,7 @@ MeshVisualizerGLBase& MeshVisualizerGLBase::setDrawOffset(const UnsignedInt offs
         "Shaders::MeshVisualizerGL::setDrawOffset(): the shader was not created with uniform buffers enabled", *this);
     CORRADE_ASSERT(offset < _drawCount,
         "Shaders::MeshVisualizerGL::setDrawOffset(): draw offset" << offset << "is out of bounds for" << _drawCount << "draws", *this);
-    setUniform(_drawOffsetUniform, offset);
+    if(_drawCount > 1) setUniform(_drawOffsetUniform, offset);
     return *this;
 }
 
@@ -426,7 +426,7 @@ MeshVisualizerGL2D::MeshVisualizerGL2D(const Flags flags
 
         #ifndef MAGNUM_TARGET_GLES2
         if(flags >= Flag::UniformBuffers) {
-            _drawOffsetUniform = uniformLocation("drawOffset");
+            if(_drawCount > 1) _drawOffsetUniform = uniformLocation("drawOffset");
         } else
         #endif
         {
@@ -757,7 +757,7 @@ MeshVisualizerGL3D::MeshVisualizerGL3D(const Flags flags
 
         #ifndef MAGNUM_TARGET_GLES2
         if(flags >= Flag::UniformBuffers) {
-            _drawOffsetUniform = uniformLocation("drawOffset");
+            if(_drawCount > 1) _drawOffsetUniform = uniformLocation("drawOffset");
         } else
         #endif
         {

src/Magnum/Shaders/MeshVisualizerGL.h

@@ -495,7 +495,9 @@ class MAGNUM_SHADERS_EXPORT MeshVisualizerGL2D: public Implementation::MeshVisua
          * @ref bindTransformationProjectionBuffer() and @ref bindDrawBuffer()
          * should be used for current draw. Expects that
          * @ref Flag::UniformBuffers is set and @p offset is less than
-         * @ref drawCount(). Initial value is @cpp 0 @ce.
+         * @ref drawCount(). Initial value is @cpp 0 @ce, if @ref drawCount()
+         * is @cpp 1 @ce, the function is a no-op as the shader assumes draw
+         * offset to be always zero.
          *
          * If @ref Flag::MultiDraw is set, @glsl gl_DrawID @ce is added to this
          * value, which makes each draw submitted via
@@ -1490,7 +1492,8 @@ class MAGNUM_SHADERS_EXPORT MeshVisualizerGL3D: public Implementation::MeshVisua
          * @ref bindTransformationBuffer() and @ref bindDrawBuffer() should be
          * used for current draw. Expects that @ref Flag::UniformBuffers is set
          * and @p offset is less than @ref drawCount(). Initial value is
-         * @cpp 0 @ce.
+         * @cpp 0 @ce, if @ref drawCount() is @cpp 1 @ce, the function is a
+         * no-op as the shader assumes draw offset to be always zero.
          *
          * If @ref Flag::MultiDraw is set, @glsl gl_DrawID @ce is added to this
          * value, which makes each draw submitted via

src/Magnum/Shaders/Phong.frag

@@ -149,6 +149,7 @@ uniform lowp float lightRanges[LIGHT_COUNT]
 
 #else
 #ifndef MULTI_DRAW
+#if DRAW_COUNT > 1
 #ifdef EXPLICIT_UNIFORM_LOCATION
 layout(location = 0)
 #endif
@@ -157,6 +158,9 @@ uniform highp uint drawOffset
     = 0u
     #endif
     ;
+#else
+#define drawOffset 0u
+#endif
 #define drawId drawOffset
 #endif
 

src/Magnum/Shaders/Phong.vert

@@ -114,6 +114,7 @@ uniform highp vec4 lightPositions[LIGHT_COUNT]
 /* Uniform buffers */
 
 #else
+#if DRAW_COUNT > 1
 #ifdef EXPLICIT_UNIFORM_LOCATION
 layout(location = 0)
 #endif
@@ -122,6 +123,9 @@ uniform highp uint drawOffset
     = 0u
     #endif
     ;
+#else
+#define drawOffset 0u
+#endif
 
 /* Keep in sync with Phong.frag. Can't "outsource" to a common file because
    the #extension directive needs to be always before any code. */

src/Magnum/Shaders/PhongGL.cpp

@@ -326,7 +326,7 @@ PhongGL::PhongGL(const Flags flags, const UnsignedInt lightCount
     {
         #ifndef MAGNUM_TARGET_GLES2
         if(flags >= Flag::UniformBuffers) {
-            _drawOffsetUniform = uniformLocation("drawOffset");
+            if(_drawCount > 1) _drawOffsetUniform = uniformLocation("drawOffset");
         } else
         #endif
         {
@@ -706,7 +706,7 @@ PhongGL& PhongGL::setDrawOffset(const UnsignedInt offset) {
         "Shaders::PhongGL::setDrawOffset(): the shader was not created with uniform buffers enabled", *this);
     CORRADE_ASSERT(offset < _drawCount,
         "Shaders::PhongGL::setDrawOffset(): draw offset" << offset << "is out of bounds for" << _drawCount << "draws", *this);
-    setUniform(_drawOffsetUniform, offset);
+    if(_drawCount > 1) setUniform(_drawOffsetUniform, offset);
     return *this;
 }
 

src/Magnum/Shaders/PhongGL.h

@@ -1296,7 +1296,9 @@ class MAGNUM_SHADERS_EXPORT PhongGL: public GL::AbstractShaderProgram {
          * bound with @ref bindTransformationBuffer(), @ref bindDrawBuffer()
          * and @ref bindTextureTransformationBuffer() should be used for
          * current draw. Expects that @ref Flag::UniformBuffers is set and
-         * @p offset is less than @ref drawCount(). Initial value is @cpp 0 @ce.
+         * @p offset is less than @ref drawCount(). Initial value is
+         * @cpp 0 @ce, if @ref drawCount() is @cpp 1 @ce, the function is a
+         * no-op as the shader assumes draw offset to be always zero.
          *
          * If @ref Flag::MultiDraw is set, @glsl gl_DrawID @ce is added to this
          * value, which makes each draw submitted via

src/Magnum/Shaders/Vector.frag

@@ -54,6 +54,7 @@ uniform lowp vec4 color
 
 #else
 #ifndef MULTI_DRAW
+#if DRAW_COUNT > 1
 #ifdef EXPLICIT_UNIFORM_LOCATION
 layout(location = 0)
 #endif
@@ -62,6 +63,9 @@ uniform highp uint drawOffset
     = 0u
     #endif
     ;
+#else
+#define drawOffset 0u
+#endif
 #define drawId drawOffset
 #endif
 

src/Magnum/Shaders/Vector.vert

@@ -76,6 +76,7 @@ uniform mediump mat3 textureMatrix
 /* Uniform buffers */
 
 #else
+#if DRAW_COUNT > 1
 #ifdef EXPLICIT_UNIFORM_LOCATION
 layout(location = 0)
 #endif
@@ -84,6 +85,9 @@ uniform highp uint drawOffset
     = 0u
     #endif
     ;
+#else
+#define drawOffset 0u
+#endif
 
 layout(std140
     #ifdef EXPLICIT_BINDING

src/Magnum/Shaders/VectorGL.cpp

@@ -164,7 +164,7 @@ template<UnsignedInt dimensions> VectorGL<dimensions>::VectorGL(const Flags flag
     {
         #ifndef MAGNUM_TARGET_GLES2
         if(flags >= Flag::UniformBuffers) {
-            _drawOffsetUniform = uniformLocation("drawOffset");
+            if(_drawCount > 1) _drawOffsetUniform = uniformLocation("drawOffset");
         } else
         #endif
         {
@@ -257,7 +257,7 @@ template<UnsignedInt dimensions> VectorGL<dimensions>& VectorGL<dimensions>::set
         "Shaders::VectorGL::setDrawOffset(): the shader was not created with uniform buffers enabled", *this);
     CORRADE_ASSERT(offset < _drawCount,
         "Shaders::VectorGL::setDrawOffset(): draw offset" << offset << "is out of bounds for" << _drawCount << "draws", *this);
-    setUniform(_drawOffsetUniform, offset);
+    if(_drawCount > 1) setUniform(_drawOffsetUniform, offset);
     return *this;
 }
 

src/Magnum/Shaders/VectorGL.h

@@ -401,7 +401,9 @@ template<UnsignedInt dimensions> class MAGNUM_SHADERS_EXPORT VectorGL: public GL
          * @ref bindDrawBuffer() and @ref bindTextureTransformationBuffer()
          * should be used for current draw. Expects that
          * @ref Flag::UniformBuffers is set and @p offset is less than
-         * @ref drawCount(). Initial value is @cpp 0 @ce.
+         * @ref drawCount(). Initial value is @cpp 0 @ce, if @ref drawCount()
+         * is @cpp 1 @ce, the function is a no-op as the shader assumes draw
+         * offset to be always zero.
          *
          * If @ref Flag::MultiDraw is set, @glsl gl_DrawID @ce is added to this
          * value, which makes each draw submitted via

src/Magnum/Shaders/VertexColor.vert

@@ -65,6 +65,7 @@ uniform highp mat4 transformationProjectionMatrix
 /* Uniform buffers */
 
 #else
+#if DRAW_COUNT > 1
 #ifdef EXPLICIT_UNIFORM_LOCATION
 layout(location = 0)
 #endif
@@ -73,6 +74,9 @@ uniform highp uint drawOffset
     = 0u
     #endif
     ;
+#else
+#define drawOffset 0u
+#endif
 
 layout(std140
     #ifdef EXPLICIT_BINDING

src/Magnum/Shaders/VertexColorGL.cpp

@@ -144,7 +144,7 @@ template<UnsignedInt dimensions> VertexColorGL<dimensions>::VertexColorGL(const
     {
         #ifndef MAGNUM_TARGET_GLES2
         if(flags >= Flag::UniformBuffers) {
-            _drawOffsetUniform = uniformLocation("drawOffset");
+            if(_drawCount > 1) _drawOffsetUniform = uniformLocation("drawOffset");
         } else
         #endif
         {
@@ -194,7 +194,7 @@ template<UnsignedInt dimensions> VertexColorGL<dimensions>& VertexColorGL<dimens
         "Shaders::VertexColorGL::setDrawOffset(): the shader was not created with uniform buffers enabled", *this);
     CORRADE_ASSERT(offset < _drawCount,
         "Shaders::VertexColorGL::setDrawOffset(): draw offset" << offset << "is out of bounds for" << _drawCount << "draws", *this);
-    setUniform(_drawOffsetUniform, offset);
+    if(_drawCount > 1) setUniform(_drawOffsetUniform, offset);
     return *this;
 }
 

src/Magnum/Shaders/VertexColorGL.h

@@ -331,7 +331,9 @@ template<UnsignedInt dimensions> class MAGNUM_SHADERS_EXPORT VertexColorGL: publ
          * @ref TransformationProjectionUniform3D buffers bound with
          * @ref bindTransformationProjectionBuffer() should be used for current
          * draw. Expects that @ref Flag::UniformBuffers is set and @p offset is
-         * less than @ref drawCount(). Initial value is @cpp 0 @ce.
+         * less than @ref drawCount(). Initial value is @cpp 0 @ce, if
+         * @ref drawCount() is @cpp 1 @ce, the function is a no-op as the
+         * shader assumes draw offset to be always zero.
          *
          * If @ref Flag::MultiDraw is set, @glsl gl_DrawID @ce is added to this
          * value, which makes each draw submitted via