graphicsdriver/opengl: Treat a texture as a uniform variable

internal/graphicsdriver/opengl/graphics.go

@@ -156,15 +156,18 @@ func (g *Graphics) Draw(indexLen int, indexOffset int, mode driver.CompositeMode
 	}
 
 	if filter == driver.FilterScreen {
-		scale := float32(g.state.destination.width) / float32(g.state.source.width)
+		scale := float32(destination.width) / float32(source.width)
 		uniforms["scale"] = scale
 	}
 
+	uniforms["texture"] = source.textureNative
+
 	if err := g.useProgram(program, uniforms); err != nil {
 		return err
 	}
 
 	g.context.drawElements(indexLen, indexOffset*2) // 2 is uint16 size in bytes
+
 	// glFlush() might be necessary at least on MacBook Pro (a smilar problem at #419),
 	// but basically this pass the tests (esp. TestImageTooManyFill).
 	// As glFlush() causes performance problems, this should be avoided as much as possible.

internal/graphicsdriver/opengl/program.go

@@ -247,7 +247,6 @@ func (g *Graphics) useProgram(program program, uniforms map[string]interface{})
 			theArrayBufferLayout.enable(&g.context, program)
 			g.context.bindBuffer(arrayBuffer, g.state.arrayBuffer)
 			g.context.bindBuffer(elementArrayBuffer, g.state.elementArrayBuffer)
-			g.context.uniformInt(program, "texture", 0)
 		}
 
 		g.state.lastProgram = program
@@ -262,19 +261,23 @@ func (g *Graphics) useProgram(program program, uniforms map[string]interface{})
 				continue
 			}
 			g.context.uniformFloat(program, key, u)
+			g.state.lastUniforms[key] = u
 		case []float32:
 			cached, ok := g.state.lastUniforms[key].([]float32)
 			if ok && areSameFloat32Array(cached, u) {
 				continue
 			}
 			g.context.uniformFloats(program, key, u)
-		}
 			g.state.lastUniforms[key] = u
-	}
-
+		case textureNative:
+			// Apparently, a texture must be bound every time. The cache is not used here.
+			// TODO: Use another value than 0 when binding multiple textures.
+			g.context.uniformInt(program, key, 0)
 			// We don't have to call gl.ActiveTexture here: GL_TEXTURE0 is the default active texture
 			// See also: https://www.opengl.org/sdk/docs/man2/xhtml/glActiveTexture.xml
-	g.context.bindTexture(g.state.source.textureNative)
+			g.context.bindTexture(u)
+		}
+	}
 
 	g.state.source = nil
 	g.state.destination = nil