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attribute vec4 a_position;
attribute vec2 a_normal;
attribute vec2 a_colorTexCoords;
uniform mat4 modelView;
uniform mat4 projection;
uniform mat4 pivotTransform;
varying vec2 v_colorTexCoords;
void main(void)
{
// Here we intentionally decrease precision of 'pivot' calculation
// to eliminate jittering effect in process of billboard reconstruction.
lowp vec4 pivot = vec4(a_position.xyz, 1.0) * modelView;
vec4 offset = vec4(a_normal, 0.0, 0.0) * projection;
float pivotZ = a_position.w;
float zScale = projection[0][0] * length(vec4(1.0, 0.0, 0.0, 0.0) * modelView);
vec4 projectedPivot = pivot * projection;
float logicZ = projectedPivot.z / projectedPivot.w;
vec4 transformedPivot = pivotTransform * vec4(projectedPivot.xy, pivotZ * zScale, projectedPivot.w);
vec4 scale = pivotTransform * vec4(1.0, -1.0, 0.0, 1.0);
gl_Position = vec4(transformedPivot.xy / transformedPivot.w, logicZ, 1.0) + vec4(offset.xy / scale.w * scale.x, 0.0, 0.0);
v_colorTexCoords = a_colorTexCoords;
}
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