Drawing RAW buffer to CGBitmapContext

Question

Hi all,

I have a raw image buffer in the RGB format. I need to draw it to CGContext so that I get a new buffer of the format ARGB. I accomplish this in the following way:

Create a data provider out of raw buffer using CGDataProviderCreateWithData and then create image out of the data provider with the api: CGImageCreate.

Now if I write this image back to the CGBitmapContext using CGContextImageDraw.

Instead of creating an intermediate image, is there any way of writing the buffer directly to CGContext so that I can avoid the image creation phase?

Thanks

Answer 1

If you are using a CGBitmapContext then you can get a pointer to the bitmap buffer using the CGBitmapContextGetData() function. You can then write your data directly to the buffer.

Answer 2

If all you want is to take RGB data with no alpha component and turn it into ARGB data with full opacity (alpha = 1.0 at all points), why not just copy the data yourself into a new buffer?

// assuming 24-bit RGB (1 byte per color component)
unsigned char *rgb = /* ... */;
size_t rgb_bytes = /* ... */;
const size_t bpp_rgb = 3;  // bytes per pixel - rgb
const size_t bpp_argb = 4;  // bytes per pixel - argb
const size_t npixels = rgb_bytes / bpp_rgb;
unsigned char *argb = malloc(npixels * bpp_argb);
for (size_t i = 0; i < npixels; ++i) {
    const size_t argbi = bpp_argb * i;
    const size_t rgbi = bpp_rgb * i;
    argb[argbi] = 0xFF;  // alpha - full opacity
    argb[argbi + 1] = rgb[rgbi];  // r
    argb[argbi + 2] = rgb[rgbi + 1];  // g
    argb[argbi + 3] = rgb[rgbi + 2];  // b
}