provide blending configuration in Renderer

Signed-off-by: Petr Babic <xbabic@fi.muni.cz>

gfx/include/gfx/renderer.hpp

@@ -63,6 +63,16 @@ struct Renderer : public com::Library {
      */
     static void gather_lights(const com::Folder *collection, std::vector<const com::Folder*> &lights);
 
+    /**
+     * Configures blending options in OpenGL.
+     * Can be used to render (partially) transparent objects.
+     * For more info, see https://docs.gl/gl3/glBlendFunc.
+     * @param enable determines whether to enable or disable blending.
+     * @param sfactor is passed to glBlendFunc.
+     * @param dfactor is passed to glBlendFunc.
+     */
+    static void configure_blending(bool enable, GLenum sfactor = GL_SRC_ALPHA, GLenum dfactor = GL_ONE_MINUS_SRC_ALPHA);
+
   protected:
     void initialize() override;
     void release() override;

gfx/src/renderer.cpp

@@ -139,6 +139,15 @@ void Renderer::gather_lights(const com::Folder *collection, std::vector<const co
     }
 }
 
+void Renderer::configure_blending(bool enable, GLenum sfactor, GLenum dfactor) {
+    if (enable) {
+        GL_ASSUME_SUCCESS(glEnable(GL_BLEND));
+        GL_ASSUME_SUCCESS(glBlendFunc(sfactor, dfactor));
+    } else {
+        GL_ASSUME_SUCCESS(glDisable(GL_BLEND));
+    }
+}
+
 void Renderer::copy_depth_buffer() const {
     auto [width, height] = detail::window_size();