How to use OpenGL's glMapBuffer in Python?

Question

I want to try updating a VBO in PyOpenGL using glMapBuffer, which returns a ctypes pointer to the mapped memory. Now, almost all the examples for this function are in C and use memcpy, which does apparently not exist in Python as such.

So, how can I update the data using this pointer?

Does this answer your question? Pointers and arrays in Python ctypes — vallentin
– vallentin, Commented Aug 26, 2020 at 9:53
@vallentin Not really, since I have virtually no experience with ctypes , and I understand neither the question nor the answer. — Parashoo
– Parashoo, Commented Aug 26, 2020 at 10:30

Rabbid76 · Accepted Answer · 2020-08-26 16:58:33Z

1

Use from_address from the ctypes to get a ctypes type instance using the memory returned by glMapBuffer.

The following example maps the buffer to an array of numberOfFloats floats:

map_data = glMapBuffer(GL_ARRAY_BUFFER, GL_WRITE_ONLY)
map_array = (GLfloat * numberOfFloats).from_address(map_data)

// copy new data
// [...]

glUnmapBuffer(GL_ARRAY_BUFFER)

The elements of map_array can be accessed by subscription:

map_array[i] = value

Data can be copied form one ctypes array to another by ctypes.memmove(dst, src, count).

edited Aug 26, 2020 at 16:58

answered Aug 26, 2020 at 13:55

Rabbid76

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