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dp3 - ps

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Computes the three-component dot product of the source registers.

Syntax

dp3 dst, src0, src1

 

where

  • dst is the destination register.
  • src0 is a source register.
  • src1 is a source register.

Remarks

Pixel shader versions 1_1 1_2 1_3 1_4 2_0 2_x 2_sw 3_0 3_sw
dp3 x x x x x x x x x

 

The following code snippet shows the operations performed:

dest.x = dest.y = dest.z = dest.w = 
  (src0.x * src1.x) + (src0.y * src1.y) + (src0.z * src1.z);

This instruction runs in the vector pipeline, always writing out to the color channels. For version 1_4, this instruction still uses the vector pipeline but may write to any channel.

An instruction with a destination register .rgb (.xyz) write mask may be co-issued with dp3 As shown below.

dp3 r0.rgb, t0, v0            // Copy scalar result to color components
+mov r2.a, t0                 // Copy alpha component from t0 in parallel

The dp3 instruction can be modified using the Source Register Signed Scaling input argument modifier (_bx2) applied to its input arguments if they are not already expanded to signed dynamic range. For a lighting shader, the saturate instruction modifier (_sat) is often used to clamp the negative values to black, as shown in the following example.

dp3_sat r0, t0_bx2, v0_bx2    // t0 is a bump map, v0 contains the light direction

Pixel Shader Instructions