if_comp (Vertex Shader)

Start an if...else...endif block, with a condition based on values that could be computed in a shader. This instruction is used to skip a block of code, based on a condition.

Syntax

Where:

• _comp is a comparison between the two source registers. It can be one of the following:

  Syntax	Comparison
  _gt	Greater than
  _lt	Less than
  _ge	Greater than or equal
  _le	Less than or equal
  _eq	Equal to
  _ne	Not equal to

• src0 is a source register. Replicate swizzle is required to select a component.
• src1 is a source register. Replicate swizzle is required to select a component.

Remarks

This instruction is used to skip a block of code, based on a condition.

if (src0 comparison src1)
   jump to the corresponding else or endif instruction;

Be careful using the equals and not equals comparison modes on floating point numbers. Because rounding occurs during during floating point calculations, the comparison can be done against an epsilon value (small nonzero number) to avoid errors.

Restrictions include:

• if_comp...else...endif blocks (along with the predicated if blocks) can be nested up to 24 layers deep.
• src0 and src1 registers require a replicate swizzle.
• if_comp blocks must end with an else or endif instruction.
• if_comp...else...endif blocks cannot straddle a loop block. The if_comp block must be completely inside, or outside the loop block.

Example

This instruction provides conditional dynamic flow control.

if_lt r3.x, r4.y
// Instructions to run if r3.x < r4.y

else
// Instructions to run otherwise

endif

Instruction Information