How to bilinear interpolate a quad

gistfile1.txt

ofVec2f rowCols[5][5];
ofVec2f texz[5][5];
int i = 0;
int j = 0;

for(float xx = 0; xx <= 1; xx += 0.25) {
  	
	// here's the meat
	ofVec2f p0_p1 = quad[0]*xx + quad[1]*(1.f-xx);
	ofVec2f p4_p3 = quad[2]*xx + quad[3]*(1.f-xx);
	
	j = 0;
	for(float yy = 0; yy <= 1; yy += 0.25) {
		
		ofVec2f p = p0_p1 * yy + p4_p3 * (1.f - yy);
	
		rowCols[i][j] = p;
		texz[i][j] = ofVec2f(xx, yy);

		j++;
	}
	i++;
}