@@ -3,25 +3,42 @@
// hellotriangle is an example Metal program that renders a single frame with a triangle.
// It writes the frame to a triangle.png file in current working directory.
package main

import (
	"flag"
	"fmt"
	"image"
	"image/png"
	"log"
	"os"
	"unsafe"

	"dmitri.shuralyov.com/gpu/mtl"
	"golang.org/x/image/math/f32"
)

func usage() {
	fmt.Fprintln(os.Stderr, "Usage: hellotriangle")
	flag.PrintDefaults()
}

func main() {
	device, err := mtl.CreateSystemDefaultDevice()
	flag.Usage = usage
	flag.Parse()

	err := run()
	if err != nil {
		log.Fatalln(err)
	}
}

func run() error {
	device, err := mtl.CreateSystemDefaultDevice()
	if err != nil {
		return err
	}

	// Create a render pipeline state.
	const source = `#include <metal_stdlib>

using namespace metal;
@@ -42,28 +59,27 @@ fragment float4 FragmentShader(Vertex in [[stage_in]]) {
	return in.color;
}
`
	lib, err := device.MakeLibrary(source, mtl.CompileOptions{})
	if err != nil {
		log.Fatalln(err)
		return err
	}
	vs, err := lib.MakeFunction("VertexShader")
	if err != nil {
		log.Fatalln(err)
		return err
	}
	fs, err := lib.MakeFunction("FragmentShader")
	if err != nil {
		log.Fatalln(err)
		return err
	}

	var rpld mtl.RenderPipelineDescriptor
	rpld.VertexFunction = vs
	rpld.FragmentFunction = fs
	rpld.ColorAttachments[0].PixelFormat = mtl.PixelFormatRGBA8UNorm
	rps, err := device.MakeRenderPipelineState(rpld)
	if err != nil {
		log.Fatalln(err)
		return err
	}

	// Create a vertex buffer.
	type Vertex struct {
		Position f32.Vec4
@@ -114,13 +130,11 @@ fragment float4 FragmentShader(Vertex in [[stage_in]]) {
	region := mtl.RegionMake2D(0, 0, texture.Width, texture.Height)
	texture.GetBytes(&img.Pix[0], uintptr(bytesPerRow), region, 0)

	// Write output image to a PNG file.
	err = writePNG("triangle.png", img)
	if err != nil {
		log.Fatalln(err)
	}
	return err
}

// writePNG encodes the image m to a named file, in PNG format.
func writePNG(name string, m image.Image) error {
	f, err := os.Create(name)