Fighting the (glDraw)Elements

webwraith · 2011-01-01T12:39:51

I'm trying to get a simple grid drawn in OpenGL for a proof of concept, but I'm having troubles. Originally, the grid was procedurally generated from a number of vertices, but I couldn't get the grid to render. I tried reducing the code to a pre-calculated 5 square verts, but I still get no grid. I'm pretty sure it's either the order of indices, or an error in my calls to render.the code that defines the 5x5 grid, and the indices for a set of triangle strips;float grid[] = { -2.f, 0.f, 2.f, -1.f, 0.f, 2.f, 0.f, 0.f, 2.f, 1.f, 0.f, 2.f, 2.f, 0.f, 2.f , -2.f, 0.f, 1.f, -1.f, 0.f, 1.f, 0.f, 0.f, 1.f, 1.f, 0.f, 1.f, 2.f, 0.f, 1.f , -2.f, 0.f, 0.f, -1.f, 0.f, 0.f, 0.f, 0.f, 0.f, 1.f, 0.f, 0.f, 2.f, 0.f, 0.f , -2.f, 0.f, -1.f, -1.f, 0.f, -1.f, 0.f, 0.f, -1.f, 1.f, 0.f, -1.f, 2.f, 0.f, -1.f , -2.f, 0.f, -2.f, -1.f, 0.f, -2.f, 0.f, 0.f, -2.f, 1.f, 0.f, -2.f, 2.f, 0.f, -2.f };unsigned short index[] = { 0, 5, 1, 6, 2, 7, 3, 8, 4, 9 , 5, 10, 6, 11, 7, 12, 8, 13, 9, 14 , 10, 15, 11, 16, 12, 17, 13, 18, 14, 19 , 15, 20, 16, 21, 17, 22, 18, 23, 19, 24 };and the code to render;glLoadIdentity(); // move the modelview matrix by 0.008 * the fine coords glTranslatef( 0.0f, -4.0f, ( 0.008f * ( float ) cam.fine_y ) * -1 ); glRotatef( angle, 1.f, 0.f, 0.f); // render the vertices in strips, which don't change their // relationships with each other. glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT ); glDrawRangeElements( GL_TRIANGLE_STRIP, 0, 9, 14, GL_UNSIGNED_SHORT, index );The "angle" variable is updated each frame, in an attempt to make sure I'm not looking in the wrong direction.I've tried glDrawElements, glDrawRangeElements, glMultiDrawElements and glDrawArray, all with no success. I get the feeling I should be using glMultiDrawArrays, but if I've done the above wrong, it would really help for someone to point out which value/variable should actually be used.I know that the screen is updating successfully, as I can get the clear colour to change during runtime.Many thanks in advance.

Graphics and GPU Programming Programming OpenGL

Started by webwraith December 31, 2010 11:53 AM

9 comments, last by webwraith 13 years, 3 months ago

webwraith

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January 01, 2011 12:39 PM

Got it, as usual I needed to muck around with the view to properly translate and rotate the mesh into view. Darn I suck at this whole 3D business... [imwithstupid]

Fighting the (glDraw)Elements

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Fighting the (glDraw)Elements

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