Variable stretchedBillboardVertShader
stretchedBillboardVertShader: "\n// Per-vertex attributes\nattribute vec3 position;\nattribute vec2 uv;\n\n// Per-instance attributes\nattribute vec3 offset;\nattribute vec4 color;\nattribute vec3 size;\nattribute float rotation;\nattribute float uvTile;\nattribute vec4 velocity;\n\n// Uniforms\nuniform mat4 world;\nuniform mat4 view;\nuniform mat4 projection;\nuniform float speedFactor;\n\n#ifdef UV_TILE\nuniform float tileCountX;\nuniform float tileCountY;\n#endif\n\n// Varyings\nvarying vec2 vUV;\nvarying vec4 vColor;\n#ifdef TILE_BLEND\nvarying vec2 vUV2;\nvarying float vTileBlend;\n#endif\n#ifdef SOFT_PARTICLES\nvarying vec4 projPosition;\nvarying float linearDepth;\n#endif\n\nvoid main() {\n float lengthFactor = velocity.w;\n float avgSize = (size.x + size.y) * 0.5;\n vec4 mvPosition = view * world * vec4(offset, 1.0);\n vec3 viewVelocity = mat3(view * world) * velocity.xyz;\n float vlength = length(viewVelocity);\n // Stretch direction is the velocity direction; only a genuinely motionless particle has none.\n // Deriving it via normalize keeps the stretch aligned even when the speed contribution is ~0\n // (e.g. speedFactor 0), instead of collapsing the whole burst onto a fixed screen axis.\n vec3 vdir = vlength > 0.000001 ? viewVelocity / vlength : vec3(0.0, 0.0, 1.0);\n mvPosition.xyz += position.y * normalize(cross(mvPosition.xyz, vdir)) * avgSize;\n // Equivalent to viewVelocity * (1.0 + lengthFactor / vlength) for moving particles, but the\n // size-based term (vdir * lengthFactor) survives when the velocity contribution vanishes.\n mvPosition.xyz -= (position.x + 0.5) * (viewVelocity + vdir * lengthFactor) * avgSize;\n gl_Position = projection * mvPosition;\n#ifdef SOFT_PARTICLES\n projPosition = gl_Position;\n linearDepth = -mvPosition.z;\n#endif\n\n #ifdef UV_TILE\n vec2 tc = vec2(tileCountX, tileCountY);\n float baseTile = floor(uvTile);\n float tileU = mod(baseTile, tc.x) / tc.x;\n float tileV = 1.0 - floor(baseTile / tc.x) / tc.y - 1.0 / tc.y;\n vUV = uv / tc + vec2(tileU, tileV);\n #ifdef TILE_BLEND\n float nextTile = ceil(uvTile);\n float nextU = mod(nextTile, tc.x) / tc.x;\n float nextV = 1.0 - floor(nextTile / tc.x) / tc.y - 1.0 / tc.y;\n vUV2 = uv / tc + vec2(nextU, nextV);\n vTileBlend = fract(uvTile);\n #endif\n #else\n vUV = uv;\n #endif\n\n vColor = color;\n}\n"