OpenGL 2D innaccuracy

BlitzMax Forums/OpenGL Module/OpenGL 2D innaccuracy

JoshK (Posted 2005) [#1]

I am writing some 2D commands, and need to draw pixel-perfect lines, points, and rectangles. Let's say the client area is 400x300, and I want to draw a line (0,0,400,0), across the very top of the viewport. 1) I set glViewport to 0,0,400,300. 2) I set glOrtho to -200,200,-150,150. 3) I draw a line ((Ax-200),(300-Ay-150),(Bx-200),(300-By-150)) or ((0-200),(300-0-150),(400-200),(300-0-150)). The line is one pixel too high, and lies offscreen. If I make a line across the very bottom, it lies offscreen as well. What is the correct mathematical change I need to make so that I can draw an arbitrary size window and get pixel-perfect results? Thanks.

AntonyWells (Posted 2005) [#2]

(Everything)-1. Scientifically speaking.

Azathoth (Posted 2005) [#3]

.

boomboommax (Posted 2005) [#4]

o_O

Najdorf (Posted 2005) [#5]

!?

TeraBit (Posted 2005) [#6]

Doesn't the way you are defining the window mean that the client area is actually 401x301. 200 + 200 and the centre point at 0,0 150 + 150 and the centre point at 0,0 Unless I misunderstand what glOrtho is doing..

Hotcakes (Posted 2005) [#7]

So this isn't fullscreen? You can't trust windowed mode, it's not official (beta, alpha, or something).