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#version 110
#extension GL_EXT_gpu_shader4 : enable
uniform bool perspective;
uniform vec2 p0;
uniform vec2 p1;
uniform vec2 p2;
uniform vec2 p3;
varying vec2 q;
varying vec2 b1;
varying vec2 b2;
varying vec2 b3;
varying vec2 vTexCoord;
void main() {
gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
if (perspective) {
float m1 = (p3.y - p0.y)/(p3.x - p0.x);
float c1 = p0.y - m1 * p0.x;
float m2 = (p1.y - p2.y)/(p1.x - p2.x);
float c2 = p2.y - m2 * p2.x;
float mid_x = (c2 - c1) / (m1 - m2);
float mid_y = m1 * mid_x + c1;
float d0 = length(vec2(mid_x - p0.x, mid_y - p0.y));
float d1 = length(vec2(p1.x - mid_x, mid_y - p1.y));
float d2 = length(vec2(p3.x - mid_x, p3.y - mid_y));
float d3 = length(vec2(mid_x - p2.x, p2.y - mid_y));
float q;
if (gl_VertexID == 0) {
q = (d1+d3)/d3;
} else if (gl_VertexID == 1) {
q = (d0+d2)/d2;
} else if (gl_VertexID == 2) {
q = (d3+d1)/d1;
} else {
q = (d2+d0)/d0;
}
gl_Position[0] *= q;
gl_Position[1] *= q;
gl_Position[3] = q;
vTexCoord = gl_MultiTexCoord0.xy;
} else {
vec2 pos;
if (gl_VertexID == 0) { // top left
pos = p2;
} else if (gl_VertexID == 1) { // top right
pos = p3;
} else if (gl_VertexID == 2) { // bottom right
pos = p1;
} else if (gl_VertexID == 3) { // bottom left
pos = p0;
}
q = pos - p0;
b1 = p1 - p0;
b2 = p2 - p0;
b3 = p0 - p1 - p2 + p3;
}
}
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