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I haven't used OpenGL for a long time and have trouble setting up a 2D screen where the upper left window coordinates are (0,0) and the width and height of the window are the max x and max y OpenGL coordinates, such that:

glBegin(GL_LINES);
glVertex2i(0,0);
glVertex2i(800, 0);
glVertex2i(0,0);
glVertex2i(0, 600);
glEnd();

does draw one line at the top of the window and one that goes down from the top. I found many examples for glOrtho(left, right, bottom, top, near, far), but none explains what I need here. I hope the question is not too trivial and you can help me.

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  • \$\begingroup\$ i've set glOrtho(0, w, h, 0, 0.0f, -1.0f) but that gives the 0,0 to the middle of the screen, no matter what other variations i try i am not able to get 0,0 to the upper left corner \$\endgroup\$ Commented Sep 4, 2022 at 9:23
  • \$\begingroup\$ The glOrtho call looks correct. Perhaps the state is wrong? I suggest to check glViewport, the matrix mode and whether or not the projection matrix is set to identity before glOrtho is called. \$\endgroup\$ Commented Sep 4, 2022 at 21:07

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