Nothing Renders to the Screen

OpenGL OpenGL: Basic Coding
1

In my code, nothing renders to the screen. Everything is fine and glError() doesn’t show anything, yet nothing will render to the dang screen. I think it might be a scope issue (glDrawElements might not be getting the index info), but I’m not sure. I passed this around to a few buddies and they can’t make heads or tails about it, so would anyone mind just pointing out the big dummy mistake that I made? Thanks!

2

I didn’t look at the entire code but just perusing the code, I noticed that player.cpp
has an array with 4 vertices and the color array has only a single RGB. You need to have 4 RGB otherwise your PC will blow a fuse.

Also your call to glDrawElements is wrong

glDrawElements(GL_TRIANGLES, sizeof(player_indices), GL_UNSIGNED_INT, 0);You need to give the number of indices, which is 4 in your case.

Besides that, which GL are you using?
If it is GL 3.2 core, then you must use VAO as well.

3

[QUOTE=V-man;1241180]I didn’t look at the entire code but just perusing the code, I noticed that player.cpp
has an array with 4 vertices and the color array has only a single RGB. You need to have 4 RGB otherwise your PC will blow a fuse.

Also your call to glDrawElements is wrong

glDrawElements(GL_TRIANGLES, sizeof(player_indices), GL_UNSIGNED_INT, 0);You need to give the number of indices, which is 4 in your case.

Besides that, which GL are you using?
If it is GL 3.2 core, then you must use VAO as well.[/QUOTE]

First of all, thanks for your answer. The glDrawElements function I misunderstand. Okay, so it’s not the amount of indices you’re using, but the amount of elements I’m drawing? Is it not two then? I’m kind of confused on this. As for the colors I should have 4 colors because 4 vertices? How come it wastes resources with only one RGB? As for the VAO suggestion, I haven’t specified which version of OpenGL to use in my code but I have a GTX 480 and it does use OpenGL 4.2, but I don’t think it’s needed. This is actually a port of some code I did a long while back and it followed this same system and it rendered correctly.

Thanks though, I’m walking one more step closer to becoming a good GL programmer.

4

It is the amount indices.
Since you want to draw 2 triangles, how many indices is that?

You are only drawing a couple of triangles and you are worried about wasting memory?

If you have created the context the old fashion way, then you aren’t forced to used VAO.

5

Then is it not 6? 3 for each Triangle? As for wasting memory, didn’t you bring that up? I didn’t know just laying down one RGB for the whole rectangle would blow a fuse. Every tutorial I’ve followed never mentions that. As for my context, I just use GLEW.

Edit:
Oh you meant because the color would only be bound to one side of the rectangle. Never mind.

6

Guess what the problem was? I forgot one comma in my player_vertices array. Nothing and nobody could detect it, but that was it. I’m surprised there wasn’t a compiler error.

7

Yes, that is correct.

Then those aren’t good tutorials.
If you are going to send vertices and color, then each vertex must have a color associated with it.
Or, if you will be submitting vertices and normals and colors, then again, each vertex must have a normal and color.
…and so on.
This is explained in the Wiki FAQ
http://www.opengl.org/wiki/FAQ#Multi_indexed_rendering

GLEW doesn’t create a context.
http://www.opengl.org/wiki/OpenGL_Loading_Library

You have only provided 1 color, which would be for the first vertex. The other 3 vertices don’t have a color and you risk crashing your system.