How to use macOS/OS X Frameworks in go

Question

For example, how to use CoreGraphics and CoreFoundation to manipulate the screen and process data on macOS.

Answer 1

Let's say we want to use CoreGraphics and CoreFoundation to capture the screen and get the image data:

package main

// To use the two libraries we need to define the respective flags, include the required header files and import "C" immediately after
import (
    // #cgo LDFLAGS: -framework CoreGraphics
    // #cgo LDFLAGS: -framework CoreFoundation
    // #include <CoreGraphics/CoreGraphics.h>
    // #include <CoreFoundation/CoreFoundation.h>
    "C"
    "image"
    "reflect"
    "unsafe"
    // other packages...
)

func main() {
    displayID := C.CGMainDisplayID()
    width := int(C.CGDisplayPixelsWide(displayID))
    height := int(C.CGDisplayPixelsHigh(displayID))
    rawData := C.CGDataProviderCopyData(C.CGImageGetDataProvider(C.CGDisplayCreateImage(displayID)))

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

    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]
        }

    C.CFRelease(rawData)

    img := &image.RGBA{Pix: imageBytes, Stride: 4 * width, Rect: image.Rect(0, 0, width, height)}

    // There we go, we can now save or process the image further
    }