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MGL_backfacing

Determines if a polygon is backfacing.

Declaration

int MGLAPI MGL_backfacing(
fix32_t dx1,
fix32_t dy1,
fix32_t dx2,
fix32_t dy2)

Prototype In

mgraph.h

Parameters

dx1 | change in x along first edge
dy1 | change in y along first edge
dx2 | change in x along second edge
dy2 | change in y along second edge

Return Value

1 if the polygon if backfacing, 0 if it is frontfacing

Description

Determine whether a polygon is backfacing given two fixed point vectors. The vectors need to be derived from two consecutive counterclockwise edges of the polygon in order for this function to return accurate results.

Note that this function is written to correctly calculate the results for screen space coordinates, which can cause overflow with a normal 16.16 fixed point multiply if this is calculated directly using calls to MGL_FixMul.

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