How to create NSBitmapImageRep from scratch?

Question

First off: I want to use NSBezierPath to draw some simple button artwork in my app, so I figure I should create an NSBitmapImageRep, get the CGImage, create an NSImage from that, and then call setImage: on the button. Correct me if I'm wrong.

So I went to see how to create an NSBitmapImage and found this: **initWithBitmapDataPlanes:pixelsWide:pixelsHigh:bitsPerSample:samplesPerPixel:hasAlpha:isPlanar:colorSpaceName:bitmapFormat:bytesPerRow:bitsPerPixel:**

Whoa.

Keeping in mind what I was looking for was something along the lines of an initWithSize:, what should I put in for those values?

Answer 1

Any particular reason you're not simply creating a new NSImage and drawing into it by bracketing your drawing code with focus locking like

NSImage* anImage = [[NSImage alloc] initWithSize:NSMakeSize(100.0,  100.0)];
[anImage lockFocus];

// Do your drawing here...

[anImage unlockFocus];

(The Cocoa Drawing Guide is your friend, btw)

Answer 2

The documentation explains it pretty well.

The planes parameter is a little confusing. It's basically a pointer to the pointer to the pixels. So if you have your pixels in an array pointed to by a variable named "pixels", like this:

unsigned char* pixels = malloc (width * height * 4); // assumes ARGB 8-bit pixels
NSBitmapImageRep* myImageRep = [[NSBitmapImageRep alloc] initWithDataPlanes:&pixels
... etc...];

The rest of the parameters are pretty straightforward. pixelWidth and pixelHeight are just what you'd expect. The other values all correspond to how your data is arranged. Are you using ARGB data at 8 bits per channel? Or is it RGBA at 32-bits per channel?

NSDeviceRGBColorSpace is probably sufficient for your uses for the color space.

The isPlanar channel should be NO if you're passing in a single pointer to your image data.

Answer 3

You don't need to allocate space for the data planes. Below is a call to create an empty 32-bit NSBitmapImageRep with an alpha component.

NSBitmapImageRep *newRep = [[NSBitmapImageRep alloc] initWithBitmapDataPlanes:NULL
                                                                   pixelsWide:pixelsWide
                                                                   pixelsHigh:pixelsHigh
                                                                bitsPerSample:8
                                                              samplesPerPixel:4
                                                                     hasAlpha:YES
                                                                     isPlanar:NO
                                                               colorSpaceName:NSDeviceRGBColorSpace
                                                                   bytesPerRow:4 * pixelsWide
                                                                  bitsPerPixel:32];