How to create a transparent canvas?

[roffe]

Im trying to create a empty transparent canvas that i can add images on.

right now i am resorting to

	c := image.NewNRGBA(rectangle)
	buf := &bytes.Buffer{}
	if err := png.Encode(buf, c); err != nil {
		panic(err)
	}
	canvas, err := vips.NewImageFromBuffer(buf.Bytes())
	if err != nil {
		panic(err)
	}

which feels toaly backwards.

I have tried using vips.Black() but it only gives me a black image and when i try to draw using img.Insert(), the whole image is still just black

if i do canvas := &vips.ImageRef{} i cannot propagate all fields needed for it to work

Any smart things i've missed in the lib?

Cheers and thanks!

[roffe]

Found this way to do it as well, but still feels very hacky :/

        // bytes for a 1x1 transparent png umage
        var tmpl = []byte{0x89, 0x50, 0x4E, 0x47, 0xD, 0xA, 0x1A, 0xA, 0x0, 0x0, 0x0, 0xD, 0x49, 0x48, 0x44, 0x52, 0x0, 0x0, 0x0, 0x1, 0x0, 0x0, 0x0, 0x1, 0x8, 0x6, 0x0, 0x0, 0x0, 0x1F, 0x15, 0xC4, 0x89, 0x0, 0x0, 0x0, 0x11, 0x49, 0x44, 0x41, 0x54, 0x78, 0x9C, 0x62, 0x62, 0x60, 0x60, 0x60, 0x0, 0x4, 0x0, 0x0, 0xFF, 0xFF, 0x0, 0xF, 0x0, 0x3, 0xFE, 0x8F, 0xEB, 0xCF, 0x0, 0x0, 0x0, 0x0, 0x49, 0x45, 0x4E, 0x44, 0xAE, 0x42, 0x60, 0x82}


	imageCount := len(images)
	canvas, err := vips.NewImageFromBuffer(tmpl)
	if err != nil {
		panic(err)
	}
	width := rectangle.Dx()
	height := rectangle.Dy()

	if err := canvas.ResizeWithVScale(float64(width), float64(height), vips.KernelAuto); err != nil {
		panic(err)
	}

[roffe]

would be nice if i just could createa image filled with alpha direcltly instead of drawing a black one, adding alpha and then filling it with a big rectangle

func newCanvas(width, height int) *vips.ImageRef {
	canvas, err := vips.Black(width, height)
	if err != nil {
		panic(err)
	}
	if err := canvas.AddAlpha(); err != nil {
		panic(err)
	}
	if err := canvas.ToColorSpace(vips.InterpretationSRGB); err != nil {
		panic(err)
	}
	if err := canvas.DrawRect(vips.ColorRGBA{R: 0, G: 0, B: 0, A: 0}, 0, 0, width, height, true); err != nil {
		panic(err)
	}
	return canvas
}

[roffe]

func newCanvas(width, height int) (*vips.ImageRef, error) {
	canvas, err := vips.Black(1, 1)
	if err != nil {
		return nil, err
	}
	if err := canvas.ToColorSpace(vips.InterpretationSRGB); err != nil {
		return nil, err
	}
	if err := canvas.AddAlpha(); err != nil {
		return nil, err
	}
	if err := canvas.Invert(); err != nil {
		return nil, err
	}
	if err := canvas.Embed(0, 0, width, height, vips.ExtendCopy); err != nil {
		return nil, err
	}
	return canvas, nil
}