blender-archive/source/blender/gpu/shaders/gpu_shader_gpencil_stroke_vert.glsl

uniform mat4 ModelViewProjectionMatrix;
uniform mat4 ProjectionMatrix;

uniform float pixsize; /* rv3d->pixsize */
uniform int keep_size;
uniform float objscale;
uniform float pixfactor;

in vec3 pos;
in vec4 color;
in float thickness;

out vec4 finalColor;
out float finalThickness;

#define TRUE 1

float defaultpixsize = pixsize * (1000.0 / pixfactor);

void main(void)
{
  gl_Position = ModelViewProjectionMatrix * vec4(pos, 1.0);
  finalColor = color;

  if (keep_size == TRUE) {
    finalThickness = thickness;
  }
  else {
    float size = (ProjectionMatrix[3][3] == 0.0) ? (thickness / (gl_Position.z * defaultpixsize)) :
                                                   (thickness / defaultpixsize);
    finalThickness = max(size * objscale, 1.0);
  }
}