Oh yes, when I think about it my pseudocode solution above is right. I was forgetting that the result was in world space, not screen space, so there are no perspective problems.

I coded it up quickly just to double check and it does indeed work.

Disclaimer: The following code is absolutely horrible and is a proof-of-concept only. Please note that it contains significant risk of divide-by-zero errors. You'll obviously need to replace Array and ImageLoader with your preferred image loading function/library. This code is hardcoded to work with an 8 by 8 BGR texture. Variables v1, v2 and v3 are the positions of the vertices of the triangle. Variables t1, t2 and t3 are the texture coordinates at those vertices.

#include <GL/glut.h>#include <GL/glext.h>#include "Array.h"#include "ImageLoader.h"GLuint texture;void display();void reshape(int width, int height);int main(int argc, char** argv){	glutInit(&argc, argv);	glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA | GLUT_STENCIL | GLUT_ALPHA);	glutInitWindowPosition(0, 0);	glutInitWindowSize(640, 480);	glutCreateWindow("Texel Position Test");	glutReshapeFunc(reshape);	glutDisplayFunc(display);	glutIdleFunc(display);	Array<unsigned char> texData = ImageLoader::loadImage("texture.bmp");	glGenTextures(1, &texture);	glBindTexture(GL_TEXTURE_2D, texture);	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 8, 8, 0, GL_BGR_EXT, GL_UNSIGNED_BYTE, (void*)texData.getRawArray());	glEnable(GL_TEXTURE_2D);	glPointSize(5);	glutMainLoop();	return 0;}void reshape(int width, int height){	GLfloat fovy = width / (float)height;	glMatrixMode(GL_PROJECTION);	glLoadIdentity();	glViewport(0, 0, width, height);	gluPerspective(45.0f,fovy,1.0f,100.0f);	glMatrixMode(GL_MODELVIEW);	glLoadIdentity();}class Point{	public:		Point(float mx = 0, float my = 0, float mz = 0)		{			x = mx;			y = my;			z = mz;		}		Point operator-(Point p) const		{			return Point(x - p.x, y - p.y, z - p.z);		}		float x, y, z;};Point solve(int x, int y, Point v1, Point v2, Point v3, Point t1, Point t2, Point t3){	float nx = (x + 0.5f) / 8.0f;	float ny = (y + 0.5f) / 8.0f;	Point vv1 = v2 - v1;	Point vv2 = v3 - v1;	Point tv1 = t2 - t1;	Point tv2 = t3 - t1;	float beta = (ny - (t1.y + ((nx * tv1.y) / tv1.x) - ((t1.x * tv1.y) / tv1.x))) / (tv2.y - ((tv2.x * tv1.y) / tv1.x));	float alpha = (nx - (t1.x + (beta * tv2.x))) / tv1.x;	Point conf(t1.x + (alpha * tv1.x) + (beta * tv2.x), t1.y + (alpha * tv1.y) + (beta * tv2.y));	return Point(v1.x + (alpha * vv1.x) + (beta * vv2.x), v1.y + (alpha * vv1.y) + (beta * vv2.y), v1.z + (alpha * vv1.z) + (beta * vv2.z));}void display(){	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);	glLoadIdentity();	glTranslatef(0, 0, -50);	glBegin(GL_TRIANGLES);		glTexCoord2f(0.3, 0.1);		glVertex3f(-13, -11, -7);		glTexCoord2f(1, 0.2);		glVertex3f(5, -12, 0);		glTexCoord2f(0.8, 0.8);		glVertex3f(11, 12, 6);	glEnd();	Point v1(-13, -11, -7);	Point v2(5, -12, 0);	Point v3(11, 12, 6);	Point t1(0.3, 0.1);	Point t2(1, 0.2);	Point t3(0.8, 0.8);	Point point = solve(6, 2, v1, v2, v3, t1, t2, t3);	glDisable(GL_DEPTH_TEST);	glDisable(GL_TEXTURE_2D);	glColor3f(0, 1, 0);	glBegin(GL_POINTS);		glVertex3f(point.x, point.y, point.z);	glEnd();	glColor3f(1, 1, 1);	glEnable(GL_TEXTURE_2D);	glEnable(GL_DEPTH_TEST);	glutSwapBuffers();}

Enigma

CoreMeltdown: thanks! I think this is what i meant, i will try it out ASAP.

[Edited by - Tree Penguin on June 25, 2004 12:42:19 PM]