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I want to know if it is possible to pass bpy.data.images["image"].as_pointer() to a C function to update image pixels directly, instead of using pixels.foreach_set() and pixels.foreach_get()

Edit:

I tried the following to change the float_buffer,but this did not work, the image stays the same. I have tried updating the image by setting the dirty flag, but this results in illegal memory access crash. I also tried calling image.update() and image.pixels.update() on the Python side hoping for a miracle lol.

void EXPORT set_all_pixels_to_white(ImBuf *buf) {
    float *pixels = buf->float_buffer.data;
    int num_pixels = buf->x * buf->y * buf->channels;
    for (int i = 0; i < num_pixels; i += buf->channels) {
        pixels[i] = 1;
        pixels[i + 1] = 0;
        pixels[i + 2] = 0;
        pixels[i + 3] = 1;
    }
}

Python side:

scene.mydll.set_all_pixels_to_red.argtypes = [POINTER(c_uint8)]
scene.mydll.set_all_pixels_to_red(byref(ctypes.c_uint8(my_image.as_pointer())))
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1 Answer 1

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From the source code that Blender Python uses to set image pixels, we can learn a thing or two:

  • The pointer you are sending to the dll refers to an Image. That is a different type than ImBuf.
  • You can get the ImBuf using BKE_image_acquire_ibuf(), so you have to mimic that function somehow in your dll.
  • An ImBuf is not always using the float_buffer. When ibuf->float_buffer.data == nullptr, it means that the image data is in ibuf->byte_buffer.data.
  • It is not guaranteed that an image has 4 channels, that's only when the image has an alpha channel. So to be completely safe when writing the pixel data, you should do something like
if (buf->channels == 4) {
  pixels[i + 3] = 1;
}

Perhaps this gives you some directions to get your code working.

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  • $\begingroup$ Thank you, exactly what I needed. I missed BKE_image_acquire_ibuf() during my search of Blender source code. $\endgroup$ Commented Dec 7, 2023 at 15:00

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