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pythonopenglctypesmemcpypyopengl

How to use OpenGL's glMapBuffer in Python?

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?

Solution

  • 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).