Redressement d'Image avec OpenGL Shader Language (GLSL)

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#extension GL_ARB_texture_rectangle : enable
uniform sampler2DRect tex;
uniform mat3x3 H;
uniform vec2 dstsize;
void main () {
  vec2 dstcoord = gl_TexCoord[0].st;
  vec3 uv = vec3( dstcoord.x/dstsize.x, dstcoord.y/dstsize.y, 1.0);
  vec3 srccoord = uv * H ;
  gl_FragColor = texture2DRect(tex, vec2(srccoord.x/srccoord.z, srccoord.y/srccoord.z));
}

Calculez H avec:

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double *getPerspectiveTransform(CvPoint2D32f *P) {
 
        double *H=calloc(18,sizeof(double));
        double *adj=H+9;
 
        double sx = (P[0].x-P[1].x)+(P[2].x-P[3].x);
        double sy = (P[0].y-P[1].y)+(P[2].y-P[3].y);
        double dx1 = P[1].x-P[2].x;
        double dx2 = P[3].x-P[2].x;
        double dy1 = P[1].y-P[2].y;
        double dy2 = P[3].y-P[2].y;
 
        double z = (dx1*dy2)-(dy1*dx2);
        double g = ((sx*dy2)-(sy*dx2))/z;
        double h = ((sy*dx1)-(sx*dy1))/z;
 
        // projection matrix
        double a=H[0]=P[1].x-P[0].x+g*P[1].x;
        double b=H[1]=P[3].x-P[0].x+h*P[3].x;
        double c=H[2]=P[0].x;
        double d=H[3]=P[1].y-P[0].y+g*P[1].y;
        double e=H[4]=P[3].y-P[0].y+h*P[3].y;
        double f=H[5]=P[0].y;
        H[6]=g;
        H[7]=h;
        H[8]=1;
        // inverse projection matrix (adjoint matrix)
        adj[0]=e-f*h;
        adj[1]=c*h-b;
        adj[2]=b*f-c*e;
        adj[3]=f*g-d;
        adj[4]=a-c*g;
        adj[5]=c*d-a*f;
        adj[6]=d*h-e*g;
        adj[7]=b*g-a*h;
        adj[8]=a*e-b*d;
 
//        printf("a %f b %f c %f d %f e %f f %f g %f h %f i 1\n",a,b,c,d,e,f,g,h);
//        printf("adj: a %f b %f c %f d %f e %f f %f g %f h %f i 1\n",adj[0],adj[1],adj[2],adj[3],adj[4],adj[5],adj[6],adj[7]);
        return H;
}