bgiClearCanvasImageShader

Removes the custom image shader from a canvas (reverts to global image shader). Searches g_canvasMap for canvasID. If found, sets canvas.activeImageShader = 0. If canvas not found, function silently does nothing. No return value.

This function resets canvas to use global image shader. Sets activeImageShader to 0 (use global). Canvas uses default image rendering after clearing. Silent failure if canvas doesn't exist. Common pattern: toggle canvas-specific rendering modes on/off.