Microsoft DirectX 8.1 (pixel shader versions 1.0, 1.1, 1.2, 1.3, 1.4)

lrp

Interpolates linearly between the second and third source registers by a proportion specified in the first source register.

lrp dest, src0, src1, src2

Registers

Argument	Description	Registers				Version
		vn	cn	tn	rn
dest	Destination register				x	1.0
				x	x	1.1, 1.2, 1.3
					x	1.4
src0, src1, src2	Source register	x	x	x	x	1.0, 1.1, 1.2, 1.3
			x		x	1.4 phase 1
		x	x		x	1.4 phase 2

To learn more about registers, see Registers.

Remarks

This instruction performs the linear interpolation based on the following formula.

dest = src0 * src1 + (1-src0) * src2
// which is the same as
dest = src2 + src0 * (src1 - src2)

Example

This example is for illustration only. The C code accompanying the shader has not been optimized for performance. It can use helper functions from the Sample Framework. The sample framework is the foundation on which many of the samples are built.

// This example combines a texture color with a diffuse color value.

// The shader is shown below.
ps.1.0              // Version instruction.
tex t0              // Declare texture.
lrp r0, t0, v0, t0  // Blend from v0 to t0 by t0 amount.

// The input colors and the output colors are shown below. The first image
// (src0) determines the amount of the second image (src1) and the third image
// (src2) that are blended to make the final image (dest). Where the first image
// is white, the second image appears in the output. Where the first image is 
// black, the third images appears in the output. Where the first is gray, the 
// final image contains color values from the second and third image.

      

// Additional code loads the texture in texture stage 0.
LPDIRECT3DDEVICE8   m_pd3dDevice;   // initialize the pointer
LPDIRECT3DTEXTURE8  m_pTexture0;    // a pointer to the texture.
TCHAR               strPath[512] = "textureFile.jpg";

D3DUtil_CreateTexture( m_pd3dDevice, strPath, &m;_pTexture0, D3DFMT_R5G6B5 );
m_pd3dDevice->SetTexture( 0, m_pTexture0 );