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dig412

Polygon appearing as triangle [Solved]

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I'm making a 3d car driving demo for my graphics course, and I've hit a maddening bug when trying to draw a 2d interface over the top. Basically when I draw this:
start2D();
	textures.bindTexture(0,speedo);
	glBegin(GL_POLYGON);
		glTexCoord2i(0,0); glVertex2i(10,10);
		glTexCoord2i(0,1); glVertex2i(10,134);
		glTexCoord2i(1,0); glVertex2i(200,10);
		glTexCoord2i(1,1); glVertex2i(200,134);
	glEnd();
end2D();


it appears like this: The polygon becomes a triangle, ignoring the top left vertex. I might be missing something obvious, but any suggestions are welcome. [Edited by - dig412 on December 6, 2009 3:38:47 PM]

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It's called backface culling.
If you orient the triangle in clockwise (CW) order, the triangle won't be drawn (by default). Orient it counter-clockwise (CCW).

glBegin(GL_QUAD);
glTexCoord2i(0,0); glVertex2i(10,10);
glTexCoord2i(1,0); glVertex2i(200,10);
glTexCoord2i(1,1); glVertex2i(200,134);
glTexCoord2i(0,1); glVertex2i(10,134);
glEnd();


4<----3
^
CCW |
|
1---->2

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Damn, I knew it was going to be something obvious!
Thanks!

I thought both of them would be culled though, since they're specified in the same direction.

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