Shaders: set default values for VertexColorShader uniforms.

Default value for matrix uniform would be zero uniform which would cause
"black screen of death".

src/Shaders/VertexColorShader.cpp

@@ -75,6 +75,11 @@ template<UnsignedInt dimensions> VertexColorShader<dimensions>::VertexColorShade
     {
         transformationProjectionMatrixUniform = uniformLocation("transformationProjectionMatrix");
     }
+
+    /* Set defaults in OpenGL ES (for desktop they are set in shader code itself) */
+    #ifdef MAGNUM_TARGET_GLES
+    setTransformationProjectionMatrix(typename DimensionTraits<dimensions>::MatrixType());
+    #endif
 }
 
 template class VertexColorShader<2>;

src/Shaders/VertexColorShader.h

@@ -57,6 +57,8 @@ template<UnsignedInt dimensions> class MAGNUM_SHADERS_EXPORT VertexColorShader:
         /**
          * @brief Set transformation and projection matrix
          * @return Pointer to self (for method chaining)
+         *
+         * Default is identity matrix.
          */
         inline VertexColorShader<dimensions>* setTransformationProjectionMatrix(const typename DimensionTraits<dimensions>::MatrixType& matrix) {
             setUniform(transformationProjectionMatrixUniform, matrix);

src/Shaders/VertexColorShader2D.vert

@@ -27,8 +27,12 @@
 #define out varying
 #endif
 
+#ifndef GL_ES
 #ifdef EXPLICIT_UNIFORM_LOCATION
-layout(location = 0) uniform mat3 transformationProjectionMatrix;
+layout(location = 0) uniform mat3 transformationProjectionMatrix = mat3(1.0);
+#else
+uniform mat3 transformationProjectionMatrix = mat3(1.0);
+#endif
 #else
 uniform highp mat3 transformationProjectionMatrix;
 #endif

src/Shaders/VertexColorShader3D.vert

@@ -27,8 +27,12 @@
 #define out varying
 #endif
 
+#ifndef GL_ES
 #ifdef EXPLICIT_UNIFORM_LOCATION
-layout(location = 0) uniform mat4 transformationProjectionMatrix;
+layout(location = 0) uniform mat4 transformationProjectionMatrix = mat4(1.0);
+#else
+uniform mat4 transformationProjectionMatrix = mat4(1.0);
+#endif
 #else
 uniform highp mat4 transformationProjectionMatrix;
 #endif