internal/graphicsdriver/opengl: record last uniform variables and reset them before swapping buffers

This is basically a revert of 6b4c696b31.
This change resets the last uniform variables before swapping
buffers.

Updates #2517

internal/graphicsdriver/opengl/graphics.go

@@ -265,6 +265,11 @@ func (g *Graphics) DrawTriangles(dstID graphicsdriver.ImageID, srcIDs [graphics.
 		g.context.ctx.Disable(gl.STENCIL_TEST)
 	}
 
+	// The last uniforms must be reset after swapping the buffer (#2517).
+	if destination.screen {
+		g.state.resetLastUniforms()
+	}
+
 	return nil
 }
 

internal/graphicsdriver/opengl/program.go

@@ -124,6 +124,7 @@ type openGLState struct {
 	elementArrayBuffer buffer
 
 	lastProgram       program
+	lastUniforms      map[string][]uint32
 	lastActiveTexture int
 }
 
@@ -135,6 +136,9 @@ func (s *openGLState) reset(context *context) error {
 
 	s.lastProgram = 0
 	context.ctx.UseProgram(0)
+	for key := range s.lastUniforms {
+		delete(s.lastUniforms, key)
+	}
 
 	// On browsers (at least Chrome), buffers are already detached from the context
 	// and must not be deleted by DeleteBuffer.
@@ -157,6 +161,25 @@ func (s *openGLState) reset(context *context) error {
 	return nil
 }
 
+func (s *openGLState) resetLastUniforms() {
+	for k := range s.lastUniforms {
+		delete(s.lastUniforms, k)
+	}
+}
+
+// areSameUint32Array returns a boolean indicating if a and b are deeply equal.
+func areSameUint32Array(a, b []uint32) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := 0; i < len(a); i++ {
+		if a[i] != b[i] {
+			return false
+		}
+	}
+	return true
+}
+
 type uniformVariable struct {
 	name  string
 	value []uint32
@@ -191,6 +214,9 @@ func (g *Graphics) useProgram(program program, uniforms []uniformVariable, textu
 		}
 
 		g.state.lastProgram = program
+		for k := range g.state.lastUniforms {
+			delete(g.state.lastUniforms, k)
+		}
 		g.state.lastActiveTexture = 0
 		g.context.ctx.ActiveTexture(gl.TEXTURE0)
 	}
@@ -206,8 +232,15 @@ func (g *Graphics) useProgram(program program, uniforms []uniformVariable, textu
 			return fmt.Errorf("opengl: length of a uniform variables %s (%s) doesn't match: expected %d but %d", u.name, typ.String(), expected, got)
 		}
 
-		// Set the uniform variables, even though they are the same as the last time (#2517).
+		cached, ok := g.state.lastUniforms[u.name]
+		if ok && areSameUint32Array(cached, u.value) {
+			continue
+		}
 		g.context.uniforms(program, u.name, u.value, u.typ)
+		if g.state.lastUniforms == nil {
+			g.state.lastUniforms = map[string][]uint32{}
+		}
+		g.state.lastUniforms[u.name] = u.value
 	}
 
 	var idx int