blender-archive/source/blender/draw/modes/shaders/object_particle_prim_vert.glsl

uniform mat4 ModelViewProjectionMatrix;
uniform mat4 ViewProjectionMatrix;
uniform mat4 ModelViewMatrix;
uniform mat4 ProjectionMatrix;
uniform int screen_space;
uniform float pixel_size;
uniform int draw_size;

in vec3 pos;
in vec4 rot;
in float val;
in vec3 inst_pos;
in int axis;

flat out int finalAxis;
flat out float finalVal;

vec3 rotate(vec3 vec, vec4 quat)
{
	/* The quaternion representation here stores the w component in the first index */
	return vec + 2.0 * cross(quat.yzw, cross(quat.yzw, vec) + quat.x * vec);
}

float mul_project_m4_v3_zfac(in vec3 co)
{
	return (ViewProjectionMatrix[0][3] * co.x) +
	       (ViewProjectionMatrix[1][3] * co.y) +
	       (ViewProjectionMatrix[2][3] * co.z) + ViewProjectionMatrix[3][3];
}

void main()
{
	float pix_size = mul_project_m4_v3_zfac(pos) * pixel_size;

	if (screen_space == 1) {
		gl_Position = ModelViewMatrix * vec4(pos, 1.0) + vec4(inst_pos * pix_size * draw_size, 0.0);
		gl_Position = ProjectionMatrix * gl_Position;
	}
	else {
		int size = draw_size;

		if (axis > -1) {
			size *= 2;
		}

		gl_Position = ModelViewProjectionMatrix * vec4(pos + rotate(inst_pos * pix_size * size, rot), 1.0);
	}

	finalAxis = axis;
	finalVal = val;
}