Interpolation

Functions related to in-primitive data interpolation. More...

Collaboration diagram for Interpolation:

Files
file	interpolation.c
file	interpolation.h
void	interpolateDepthAndWTriangle (SRPVertexShaderOut *vertices, const float *weights, const float *invW, const SRPShaderProgram *sp, float *depth, float *reciprocalInterpolatedInvW)

Detailed Description

Functions related to in-primitive data interpolation.

Function Documentation

interpolateDepthAndWTriangle()

void interpolateDepthAndWTriangle	(	SRPVertexShaderOut *	vertices,
		const float *	weights,
		const float *	invW,
		const SRPShaderProgram *	sp,
		float *	depth,
		float *	reciprocalInterpolatedInvW
	)

Let \( v_0, v_1, v_2 \) be points in space that form a triangle and \( a, b, c \) be barycentric coordinates for a point \( P \) according to \( v_0, v_1, v_2 \) respectively. Then, by the property of barycentric coordinates \( P = av_0 + bv_1 + cv_2 \). This can be extrapolated to arbitrary values assigned to vertices, and this is called affine attribute interpolation.

But this method does not take the perspective divide into account, so the texture (for example) will look "wrong".

It can be shown (see the "see also" section) that perspective-correct Z value can be obtained by dividing affinely-interpolated Ai/Wi by affinely-interpolated 1/Wi.

See also

https://www.comp.nus.edu.sg/%7Elowkl/publications/lowk_persp_interp_techrep.pdf

https://www.youtube.com/watch?v=F5X6S35SW2s

Interpolate the depth and inverse W values inside the triangle

Parameters

[in]	vertices	Array of vertices
[in]	weights	Array of barycentric coordinates
[in]	invW	Array of inverseW values for each corresponding vertex
[in]	sp	The SRPShaderProgram being used
[out]	depth	Where interpolated depth will be stored
[out]	reciprocalInterpolatedInvW	Where the reciprocal of interpolated inverse W_clip will be stored