avoid some opengl redundant calls

src/framework/graphics/graphics.cpp

@@ -76,6 +76,9 @@ void Graphics::init()
         g_painterOGL2 = new PainterOGL2;
 #endif
 
+    // blending is always enabled
+    glEnable(GL_BLEND);
+
     // determine max texture size
     static GLint maxTextureSize = -1;
     if(maxTextureSize == -1)
@@ -213,7 +216,6 @@ void Graphics::beginRender()
 
 void Graphics::endRender()
 {
-    glFlush();
 }
 
 void Graphics::setViewportSize(const Size& size)

src/framework/graphics/painter.cpp

@@ -105,13 +105,14 @@ void Painter::setTexture(Texture* texture)
     m_texture = texture;
 
     if(texture) {
-        m_glTextureId = texture->getId();
         setTextureMatrix(texture->getTransformMatrix());
-    } else
-        m_glTextureId = 0;
-    m_texture = texture;
 
-    updateGlTexture();
+        GLuint glTextureId = texture->getId();
+        if(glTextureId != m_glTextureId) {
+            m_glTextureId = glTextureId;
+            updateGlTexture();
+        }
+    }
 }
 
 void Painter::updateGlTexture()