I am trying to make a 2D game and I need to know how to find/calculate/define the edges of my screen. Aka: I want to know how big to make my triangles so the textures aren't warped and that a pixel on the texture is it's own single pixel on the screen.

I dont care how to determine this, other than brute forcing it (such as creating a triangle, and if it's too small, increase the length/width by .001 to see if it made a difference). So, if there's a function I could use to declare that i want the left edge of the screen to be -10, the right edge to be 10, the top edge to be 4 and the bottom edge to be -4, i'd be happy.

Things to note: I am planning on using an orthographic perspective, if that helps at all.