Why am I getting a BAD_ACCESS fault when calling draw functions on a CGContext used for an OpenGL texture?

Question

I am trying to create an OpenGL texture using Core Graphics. My code setup is in prepareOpenGL(). While drawing to the initialized CGContext, I get a EXC_BAD_ACCESS fault. However, when I po the context in LLDB (po context!, see below), I get an address with all of the CGContext's information. I have tried calling an expression through LLDB as well, and the output is nil. Address sanitizer, thread sanitizer, and zombies were non-revealing. My question is why is the CGContext being stated as nil, EXC_BAD_ACCESS, when the Optional<CGContext> is not nil? I have tried calling this code in drawRect(_:), but I get the same results.

import Cocoa
import CoreGraphics
import OpenGL.GL3

class MyView: NSOpenGLView {
    var textureTBO: GLuint = 0

    override func prepareOpenGL() {
        let bitmapRows = 10
        let bitmapColumns = 10
        let floatsPerPoint = 4
        var bitmapBuffer = UnsafeMutablePointer<CGFloat>.allocate(capacity: bitmapRows * bitmapColumns * floatsPerPoint)

        if let context = CGContext(data: &bitmapBuffer,
                                width: bitmapColumns,
                                height: bitmapRows,
                                bitsPerComponent: 8,
                                bytesPerRow: bitmapColumns * floatsPerPixel,
                                space: CGColorSpaceCreateDeviceRGB(),
                                bitmapInfo: CGImageAlphaInfo.noneSkipLast.rawValue) {
            context.setFillColor(red: 0, green: 0, blue: 1, alpha: 0.5)
            context.fill(CGRect(x: 0, y: 0, width: 5, height: 5))       //=>  EXC_BAD_ACCESS, code=2
            context.setFillColor(red: 1, green: 0, blue: 1, alpha: 0.5)
            context.fill(CGRect(x: 5, y: 5, width: 5, height: 5))
            context.setFillColor(red: 0, green: 1, blue: 0, alpha: 0.5)
            context.fill(CGRect(x: 0, y: 5, width: 5, height: 5))
            context.setFillColor(red: 0.5, green: 0, blue: 0.5, alpha: 0.5)
            context.fill(CGRect(x: 5, y: 0, width: 5, height: 5))
        
            glGenTextures(1, &textureTBO)
            glBindTexture(GLenum(GL_TEXTURE_2D), textureTBO)
            glTexParameteri(GLenum(GL_TEXTURE_2D), GLenum(GL_TEXTURE_MIN_FILTER), GL_LINEAR)
            glTexParameteri(GLenum(GL_TEXTURE_2D), GLenum(GL_TEXTURE_MAG_FILTER), GL_LINEAR)
            glTexParameteri(GLenum(GL_TEXTURE_2D), GLenum(GL_TEXTURE_WRAP_S), GL_REPEAT)
            glTexParameteri(GLenum(GL_TEXTURE_2D), GLenum(GL_TEXTURE_WRAP_T), GL_REPEAT)
        }

        glTexImage2D(GLenum(GL_TEXTURE_2D), 0, GLint(GL_RGB), 256, 256, 0, GLenum(GL_RGBA), GLenum(GL_UNSIGNED_INT), &bitmapBuffer)

        bitmapBuffer.deallocate()
    }
}

LLDB output - the optional is not nil

(lldb) po context!
<CGContext 0x7b3000000300> (kCGContextTypeBitmap)
    <<CGColorSpace 0x7b1800002280> (kCGColorSpaceDeviceRGB)>
        width = 256, height = 256, bpc = 8, bpp = 32, row bytes = 2048 
        kCGImageAlphaNoneSkipLast | 0 (default byte order)

LLDB output - is this telling me that a color cannot be set because the context actually is nil?

(lldb) expression context?.setFillColor(red: 0, green: 0, blue: 1, alpha: 0.5)
(Void?) $R4 = nil

LLDB output - an exercise in futility: doing the same thing and expecting a different result, haha

(lldb) expression context?.fill(CGRect(x: 0, y: 0, width: 5, height: 5))
error: Execution was interrupted, reason: EXC_BAD_ACCESS (code=2, address=0x7b08000c7ff0).
The process has been returned to the state before expression evaluation.

It seems that this can be done as I found this answer. I appreciate your thoughts, thank you!

Answer 1

data: &bitmapBuffer is a pointer to the pointer to the buffer. Replace it with data: bitmapBuffer.

Not related to the crash but 8 bits per component fits in UInt8:

var bitmapBuffer = UnsafeMutablePointer<UInt8>.allocate(capacity: bitmapRows * bitmapColumns * floatsPerPoint)