all: clean up code, upgrade to modern Go

Signed-off-by: ddkwork

gpu/internal/driver/driver.go

@@ -96,8 +96,10 @@ type BlendFactor uint8
 
 type Topology uint8
 
-type TextureFilter uint8
-type TextureFormat uint8
+type (
+	TextureFilter uint8
+	TextureFormat uint8
+)
 
 type BufferBinding uint8
 
@@ -217,7 +219,7 @@ func flipImageY(stride, height int, pixels []byte) {
 	// Flip image in y-direction. OpenGL's origin is in the lower
 	// left corner.
 	row := make([]uint8, stride)
-	for y := 0; y < height/2; y++ {
+	for y := range height / 2 {
 		y1 := height - y - 1
 		dest := y1 * stride
 		src := y * stride