cocos-enhance-kit/engine/cocos2d/renderer/build/chunks/shader/particle-common.inc

uniform Constants{
    vec4 mainTiling_Offset;
    vec4 frameTile_velLenScale;
    vec4 scale;
};

#include <cc-global>
#include <cc-local>
#include <transform>

out vec2 uv;
out vec4 color;

void computeVertPos(inout vec4 pos, vec2 vertOffset, vec4 q, vec3 s
#if CC_USE_BILLBOARD || CC_USE_VERTICAL_BILLBOARD
    , mat4 viewInv
#endif
#if CC_USE_STRETCHED_BILLBOARD
    , vec3 eye
    , vec4 velocity
    , float velocityScale
    , float lengthScale
    , float xIndex
#endif
) {
#if CC_USE_BILLBOARD
    vec3 viewSpaceVert = vec3(vertOffset.x * s.x, vertOffset.y * s.y, 0.);
    vec3 camX = normalize(vec3(viewInv[0][0], viewInv[1][0], viewInv[2][0]));
    vec3 camY = normalize(vec3(viewInv[0][1], viewInv[1][1], viewInv[2][1]));
    vec3 camZ = normalize(vec3(viewInv[0][2], viewInv[1][2], viewInv[2][2]));
    pos.xyz += rotateInLocalSpace(viewSpaceVert, camX, camY, camZ, q);
#elif CC_USE_STRETCHED_BILLBOARD
    vec3 camRight = normalize(cross(pos.xyz - eye, velocity.xyz)) * s.x;
    vec3 camUp = velocity.xyz * velocityScale + normalize(velocity.xyz) * lengthScale * s.y;
    pos.xyz += (camRight * abs(vertOffset.x) * sign(vertOffset.y)) - camUp * xIndex;
#elif CC_USE_HORIZONTAL_BILLBOARD
    vec3 viewSpaceVert = vec3(vertOffset.x * s.x, vertOffset.y * s.y, 0.);
    vec3 camX = vec3(1, 0, 0);
    vec3 camY = vec3(0, 0, -1);
    pos.xyz += rotateInLocalSpace(viewSpaceVert, camX, camY, cross(camX, camY), q);
#elif CC_USE_VERTICAL_BILLBOARD
    vec2 viewSpaceVert = vec2(vertOffset.x * s.x, vertOffset.y * s.y);
    rotateCorner(viewSpaceVert, q.z);
    vec3 camX = normalize(vec3(cc_matView[0][0], cc_matView[1][0], cc_matView[2][0]));
    vec3 camY = vec3(0, 1, 0);
    vec3 offset = camX * viewSpaceVert.x + camY * viewSpaceVert.y;
    pos.xyz += offset;
#else
    pos.x += vertOffset.x;
    pos.y += vertOffset.y;
#endif
}

vec2 computeUV(float frameIndex, vec2 vertIndex, vec2 frameTile){
    vec2 aniUV = vec2(0, floor(frameIndex * frameTile.y));
    aniUV.x = floor(frameIndex * frameTile.x * frameTile.y - aniUV.y * frameTile.x);
#if !CC_USE_MESH
    vertIndex.y = 1. - vertIndex.y; // if using billboard ,y must be flipped.but mesh does not,why?
#endif
    return (aniUV.xy + vertIndex) / vec2(frameTile.x, frameTile.y);
}