go 26 January 2025

• A binding for SDL2 exists already for Go, so there is no need to use the C functions directly
• A simple program to run a window and color it didn’t work out of the box and SDL_VIDEODRIVER=wayland needs to be set.
• The functions that takes structs as first parameter are adapted in the binding to be a method to the struct.

Simple colored window ¶

Adapted from SDL2 tutorial. It opens a window, color it light red and wait for 3 seconds before closing.

 1package main
 2
 3import (
 4	"log/slog"
 5	"os"
 6	"time"
 7
 8	"github.com/veandco/go-sdl2/sdl"
 9)
10
11func main() {
12	slog.Info("Initializing...")
13	ErrAndExit("Failed to initialize SDL", sdl.Init(sdl.INIT_EVERYTHING))
14	defer sdl.Quit()
15
16	w, err := sdl.CreateWindow("Example", sdl.WINDOWPOS_UNDEFINED, sdl.WINDOWPOS_UNDEFINED, 1280, 720, sdl.WINDOWEVENT_SHOWN)
17	ErrAndExit("Failed to create a window", err)
18	defer w.Destroy()
19
20	s, err := w.GetSurface()
21	ErrAndExit("Failed to get window surface", err)
22
23	ErrAndExit("Failed to fill rect", s.FillRect(nil, sdl.MapRGB(s.Format, 255, 90, 120)))
24	ErrAndExit("Failed to update surface", w.UpdateSurface())
25
26	time.Sleep(time.Second * 3)
27}
28
29func ErrAndExit(msg string, err error) {
30	if err != nil {
31		slog.Error("Failed to update surface", "error", err)
32		os.Exit(1)
33	}
34}

It needs to run using the following command otherwise the window appears black:

1SDL_VIDEODRIVER=wayland  go run main.go

The output looks like the following

2025/01/26 12:40:32 INFO Initializing...

Press Q to exit ¶

Replace time.Sleep with the following, will exit when q is pressed or the program gets a quit signal from the system

 1for {
 2    switch e := sdl.PollEvent().(type) {
 3    case *sdl.QuitEvent:
 4        os.Exit(0)
 5    case *sdl.KeyboardEvent:
 6        if e.Keysym.Sym == sdl.K_q {
 7            os.Exit(0)
 8        }
 9    }
10}

Load an Image ¶

Before updating the surface we can load an image and draw it

1i, err := sdl.LoadBMP("image.bmp")
2ErrAndExit("Failed to load image", err)
3defer i.Free()
4
5ErrAndExit("Failed to draw image", i.Blit(nil, s, &sdl.Rect{X: 0, Y: 0}))

Switch to GPU rendering ¶

We need to change our approach. replace the part from creating the window until we update the surface with the following

 1w, r, err := sdl.CreateWindowAndRenderer(1280, 720, sdl.WINDOWEVENT_SHOWN)
 2ErrAndExit("Failed to create a window", err)
 3defer w.Destroy()
 4defer r.Destroy()
 5
 6r.SetDrawColor(255, 90, 120, 0)
 7ErrAndExit("Failed to fill rect", r.FillRect(nil))
 8
 9i, err := sdl.LoadBMP("image.bmp")
10ErrAndExit("Failed to load image", err)
11defer i.Free()
12
13t, err := r.CreateTextureFromSurface(i)
14ErrAndExit("Failed to create texture", err)
15
16r.Copy(t, nil, nil)
17r.Present()

Switch to Go image stdlib ¶

This function loads an image and convert it to SDL surface. It can be used instead of sdl.LoadBMP so there is no need for SDL image

 1func loadImageAsSurface(filePath string) (*sdl.Surface, error) {
 2	file, err := os.Open(filePath)
 3	ErrAndExit("Failed to open image", err)
 4	defer file.Close()
 5
 6	img, _, err := image.Decode(file)
 7	ErrAndExit("Failed to decode image", err)
 8
 9	bounds := img.Bounds()
10	width, height := bounds.Dx(), bounds.Dy()
11
12	surface, err := sdl.CreateRGBSurfaceWithFormat(0, int32(width), int32(height), 32, sdl.PIXELFORMAT_ABGR8888)
13	ErrAndExit("Failed to create surface", err)
14
15	surface.Lock()
16
17	for y := 0; y < height; y++ {
18		for x := 0; x < width; x++ {
19			surface.Set(x, y, img.At(x, y))
20		}
21	}
22
23	surface.Unlock()
24
25	return surface, nil
26}

Hello world text ¶

Init TTF, Load a font, print hello world to a surface, convert it to texture and draw it

 1ErrAndExit("Failed to initialize TTF", ttf.Init())
 2defer ttf.Quit()
 3
 4f, err := ttf.OpenFont("/usr/share/fonts/inter/InterVariable.ttf", 32)
 5ErrAndExit("Failed to open fond", err)
 6defer f.Close()
 7
 8txt, err := f.RenderUTF8Solid("Hello world", sdl.Color{R: 255, G: 255, B: 255})
 9ErrAndExit("Failed to render text", err)
10defer txt.Free()
11
12txtt, err := r.CreateTextureFromSurface(txt)
13ErrAndExit("Failed to convert text surface to texture", err)
14defer txtt.Destroy()
15
16r.Copy(txtt, nil, &sdl.Rect{X: 10, Y: 10, W: txt.W, H: txt.H})

Vsync ¶

Split creating the window and renderer to be able to pass flags for VSYNC

1w, err := sdl.CreateWindow("Example", sdl.WINDOWPOS_UNDEFINED, sdl.WINDOWPOS_UNDEFINED, 1280, 720, sdl.WINDOWEVENT_SHOWN)
2ErrAndExit("Failed to create a window", err)
3defer w.Destroy()
4
5r, err := sdl.CreateRenderer(w, -1, sdl.RENDERER_ACCELERATED|sdl.RENDERER_PRESENTVSYNC)
6ErrAndExit("Failed to create renderer", err)
7defer r.Destroy()

References ¶

• SDL2 tutorial

See Also