go-sdl2 example. Paint RGBA image

paintimage.go

package main

import (
	"fmt"
	"github.com/veandco/go-sdl2/sdl"
	"image"
	"image/color"
	"math/rand"
	"unsafe"
)

func paintImage(img *image.RGBA, window *sdl.Window, destX, destY int) {
	surface, _ := window.GetSurface()
	surface.Lock()
	defer surface.Unlock()

	w, h := img.Bounds().Dx(), img.Bounds().Dy()
	surfW, surfH := int(surface.W), int(surface.H)

	for y := 0; y < h; y++ {
		for x := 0; x < w; x++ {
			sx, sy := destX+x, destY+y
			if sx < 0 || sy < 0 || sx >= surfW || sy >= surfH {
				continue
			}
			offset := img.PixOffset(x, y)
			r := img.Pix[offset+0]
			g := img.Pix[offset+1]
			b := img.Pix[offset+2]
			a := img.Pix[offset+3]
			color := sdl.MapRGBA(surface.Format, r, g, b, a)

			pixels := surface.Pixels()
			ptr := uintptr(unsafe.Pointer(&pixels[0]))
			pitch := int(surface.Pitch)
			pxOffset := sy*pitch + sx*4 // RGBA32bit
			*(*uint32)(unsafe.Pointer(ptr + uintptr(pxOffset))) = color
		}
	}
		window.UpdateSurface()
}

func main() {
	var (
		winTitle  string = "Surface Example"
		winWidth  int32  = 800
		winHeight int32  = 600
		window    *sdl.Window
		event     sdl.Event
		running   bool = true
	)

	img := image.NewRGBA(image.Rect(0, 0, 200, 200))
	for y := 0; y < 200; y++ {
		for x := 0; x < 200; x++ {
			img.Set(x, y, color.RGBA{R: uint8(x), G: uint8(y), B: 128, A: 255})
		}
	}

	if err := sdl.Init(sdl.INIT_VIDEO); err != nil {
		fmt.Println("Failed to initialize SDL:", err)
		return
	}
	defer sdl.Quit()

	window, err := sdl.CreateWindow(winTitle, sdl.WINDOWPOS_UNDEFINED, sdl.WINDOWPOS_UNDEFINED, winWidth, winHeight, sdl.WINDOW_SHOWN)
	if err != nil {
		fmt.Println("Failed to create window:", err)
		return
	}
	defer window.Destroy()


	paintImage(img, window, 0, 0)

	// Event loop
	for running {
		for event = sdl.PollEvent(); event != nil; event = sdl.PollEvent() {
			switch event.(type) {
			case *sdl.QuitEvent:
				running = false
				break
			}
		}
		sdl.Delay(16) // ~60 FPS
		x := rand.Intn(600)
		y := rand.Intn(400)
		paintImage(img, window, x, y)
	}
}