Shaders: ability to specify background color in Vector shader.

Makes it possible to use the shader without blending.

src/Shaders/Vector.cpp

@@ -38,7 +38,7 @@ namespace {
     template<> constexpr const char* vertexShaderName<3>() { return "AbstractVector3D.vert"; }
 }
 
-template<UnsignedInt dimensions> Vector<dimensions>::Vector(): transformationProjectionMatrixUniform(0), colorUniform(1) {
+template<UnsignedInt dimensions> Vector<dimensions>::Vector(): transformationProjectionMatrixUniform(0), backgroundColorUniform(1), colorUniform(2) {
     Utility::Resource rs("MagnumShaders");
 
     #ifndef MAGNUM_TARGET_GLES
@@ -76,6 +76,7 @@ template<UnsignedInt dimensions> Vector<dimensions>::Vector(): transformationPro
     #endif
     {
         transformationProjectionMatrixUniform = AbstractShaderProgram::uniformLocation("transformationProjectionMatrix");
+        backgroundColorUniform = AbstractShaderProgram::uniformLocation("backgroundColor");
         colorUniform = AbstractShaderProgram::uniformLocation("color");
     }
 

src/Shaders/Vector.frag

@@ -29,8 +29,10 @@
 #endif
 
 #ifdef EXPLICIT_UNIFORM_LOCATION
-layout(location = 1) uniform vec4 color;
+layout(location = 1) uniform vec4 backgroundColor;
+layout(location = 2) uniform vec4 color;
 #else
+uniform lowp vec4 backgroundColor;
 uniform lowp vec4 color;
 #endif
 
@@ -48,5 +50,5 @@ out lowp vec4 fragmentColor;
 
 void main() {
     lowp float intensity = texture(vectorTexture, fragmentTextureCoordinates).r;
-    fragmentColor = intensity*color;
+    fragmentColor = mix(backgroundColor, color, intensity);
 }

src/Shaders/Vector.h

@@ -56,9 +56,23 @@ template<UnsignedInt dimensions> class MAGNUM_SHADERS_EXPORT Vector: public Abst
             return *this;
         }
 
+        /**
+         * @brief Set background color
+         * @return Reference to self (for method chaining)
+         *
+         * Default is transparent black.
+         * @see @ref setColor()
+         */
+        Vector& setBackgroundColor(const Color4& color) {
+            AbstractShaderProgram::setUniform(backgroundColorUniform, color);
+            return *this;
+        }
+
         /**
          * @brief Set fill color
          * @return Reference to self (for method chaining)
+         *
+         * @see @ref setBackgroundColor()
          */
         Vector& setColor(const Color4& color) {
             AbstractShaderProgram::setUniform(colorUniform, color);
@@ -67,6 +81,7 @@ template<UnsignedInt dimensions> class MAGNUM_SHADERS_EXPORT Vector: public Abst
 
     private:
         Int transformationProjectionMatrixUniform,
+            backgroundColorUniform,
             colorUniform;
 };