screenshot_darwin.go

package screenshot

import (
	// #cgo LDFLAGS: -framework CoreGraphics
	// #cgo LDFLAGS: -framework CoreFoundation
	// #include <CoreGraphics/CoreGraphics.h>
	// #include <CoreFoundation/CoreFoundation.h>
	"C"
	"fmt"
	"image"
	"math"
	"reflect"
	"unsafe"
)

func ScreenRect() (image.Rectangle, error) {
	displayID := C.CGMainDisplayID()
	width := int(C.CGDisplayPixelsWide(displayID))
	height := int(C.CGDisplayPixelsHigh(displayID))
	return image.Rect(0, 0, width, height), nil
}

func CaptureScreen() (*image.RGBA, error) {
	rect, err := ScreenRect()
	if err != nil {
		return nil, err
	}
	return CaptureRect(rect)
}

func CaptureRect(rect image.Rectangle) (*image.RGBA, error) {
	displayID := C.CGMainDisplayID()
	width := int(math.Ceil(float64(C.CGDisplayPixelsWide(displayID))/16) * 16)

	// the three variables below are named after their CoreFoundation and
	// CoreGraphics types for ease of reference; all are of type uintptr in Go
	cgImageRef := C.CGDisplayCreateImage(displayID)
	if cgImageRef == 0 {
		return nil, fmt.Errorf("CGDisplayCreateImage(%d) returned null", displayID)
	}
	defer C.CGImageRelease(C.CGImageRef(cgImageRef))

	cgDataProviderRef := C.CGImageGetDataProvider(cgImageRef)
	if cgDataProviderRef == 0 {
		return nil, fmt.Errorf("CGImageGetDataProvider returned null")
	}
	defer C.CFRelease(C.CFTypeRef(cgDataProviderRef))

	cfDataRef := C.CGDataProviderCopyData(cgDataProviderRef)
	if cfDataRef == 0 {
		return nil, fmt.Errorf("CGDataProviderCopyData returned null")
	}
	defer C.CFRelease(C.CFTypeRef(cfDataRef))

	length := int(C.CFDataGetLength(cfDataRef))
	ptr := unsafe.Pointer(C.CFDataGetBytePtr(cfDataRef))

	var slice []byte
	hdrp := (*reflect.SliceHeader)(unsafe.Pointer(&slice))
	hdrp.Data = uintptr(ptr)
	hdrp.Len = length
	hdrp.Cap = length

	imageBytes := make([]byte, length)

	for i := 0; i < length; i += 4 {
		imageBytes[i], imageBytes[i+2], imageBytes[i+1], imageBytes[i+3] = slice[i+2], slice[i], slice[i+1], slice[i+3]
	}

	img := &image.RGBA{Pix: imageBytes, Stride: 4 * width, Rect: rect}
	return img, nil
}