// place this code into raylib/src/rcore.c
void customBeginMode3D(Camera camera)
{
    rlDrawRenderBatchActive();      // Update and draw internal render batch

    rlMatrixMode(RL_PROJECTION);    // Switch to projection matrix
    rlPushMatrix();                 // Save previous matrix, which contains the settings for the 2d ortho projection
    rlLoadIdentity();               // Reset current matrix (projection)

    float aspect = ((float)CORE.Window.currentFbo.width / 2.0f)/(float)CORE.Window.currentFbo.height;

    // NOTE: zNear and zFar values are important when computing depth buffer values
    if (camera.projection == CAMERA_PERSPECTIVE)
    {
        // Setup perspective projection
        double top = RL_CULL_DISTANCE_NEAR*tan(camera.fovy*0.5*DEG2RAD);
        double right = top*aspect;

        rlFrustum(-right, right, -top, top, RL_CULL_DISTANCE_NEAR, RL_CULL_DISTANCE_FAR);
    }
    else if (camera.projection == CAMERA_ORTHOGRAPHIC)
    {
        // Setup orthographic projection
        double top = camera.fovy/2.0;
        double right = top*aspect;

        rlOrtho(-right, right, -top,top, RL_CULL_DISTANCE_NEAR, RL_CULL_DISTANCE_FAR);
    }

    rlMatrixMode(RL_MODELVIEW);     // Switch back to modelview matrix
    rlLoadIdentity();               // Reset current matrix (modelview)

    // Setup Camera view
    Matrix matView = MatrixLookAt(camera.position, camera.target, camera.up);
    rlMultMatrixf(MatrixToFloat(matView));      // Multiply modelview matrix by view matrix (camera)

    rlEnableDepthTest();            // Enable DEPTH_TEST for 3D
}