VertexIdRewrite.h file

Shared rewrite of the engine's gl_VertexID quad-synthesis expressions into reads of vertex attributes, for the emitters targeting a stage language that has no vertex-ID input.

Two backends need exactly the same substitution, which is why it lives here rather than in either of them: the ESSL 100 profile (OpenGL|ES 2.0 has no gl_VertexID, and ESSL 100 additionally has no integer bit/modulo operators) and the Cg dialect emitted for the PS Vita's sceGxm backend (the GXM parameter semantics are the fixed-function-era Cg set — POSITION, TEXCOORD, COLOR, NORMAL, … — with no vertex-index semantic at all, so the corner cannot be recomputed in-shader there either).

Because both consumers substitute the identical expressions, a shader that works on the ES 2.0 profile keeps working on GXM: the runtime already supplies the aQuadCorner / aInstanceIndex attribute streams for the ES 2.0 profile, which the PS Vita build has always used, so the GXM vertex layout is the one the engine already produces.

Namespaces

namespace ShaderCompiler
namespace ShaderCompiler::VertexIdRewrite

Functions

auto FindSubstring(StringView haystack, StringView needle) -> std::size_t: Byte offset of needle in haystack, or Npos.
auto ReplaceAllOf(StringView s, StringView from, StringView to) -> String: Replaces every occurrence of from in s with to.
auto Apply(StringView src, bool& usedCorner, bool& usedInstance) -> String

Variables

std::size_t Npos constexpr: "Not found" sentinel of the string helpers below

Function documentation

String Apply(StringView src, bool& usedCorner, bool& usedInstance)

Rewrites the engine's gl_VertexID quad-synthesis expressions into reads of the vertex attributes the runtime supplies (a static per-vertex [0,1]² corner, and a per-vertex instance index for the batched six-vertices-per-sprite path). Sets usedCorner / usedInstance so the caller declares only the attributes that end up referenced.

Every single-quad formula is a function of the two terms float(id>>1) and float(id%2); substituting them with (1 - aQuadCorner.x) and aQuadCorner.y reproduces the exact corner of any of them (plain sprite, Lighting's 0.5-offset, TouchCircle) after constant folding, given the runtime supplies aQuadCorner = {(1,0),(1,1),(0,0),(0,1)} for the 4-vertex strip. The batched corner + instance index are fixed expressions replaced wholesale.