Using pixel coordinates for VBO data? (instead of a float -1 through 1) [SOLVED]

[shadowstryker10]

Whenever I try drawing a quad using a VBO, I have to use a float between -1 and 1, with coordinate 0, 0 being the center of the screen. Is there any way I can get it to use pixel coordinates with (0, 0) being at the bottom left of the screen instead of the middle? I tried using glOrtho like I would with immediate rendering, but the only thing that affects the VBO with glOrtho is the zNear and zFar.

Here's my code so far (I just started learning VBOs):

OpenGL Setup

glViewport(0, 0, Display.getWidth(), Display.getHeight());
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glOrtho(0, Display.getWidth(), 0, Display.getHeight(), 0, 0);
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();

	glEnable(GL_TEXTURE_2D);
	glEnable(GL_BLEND);
	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

Creating vertex/color data:

amountOfVertices = 4;
	vertexSize = 2;
	colorSize = 3;
		
	// Create buffer with vertex data
	FloatBuffer vertexData = BufferUtils.createFloatBuffer(amountOfVertices * vertexSize);
	vertexData.put(new float[] { 
			0, 0, 
			0, -1, 
			-1, -1, 
			-1, 0});
	vertexData.flip();
		
	// Create buffer with color data
	FloatBuffer colorData = BufferUtils.createFloatBuffer(amountOfVertices * colorSize);
	colorData.put(new float[] {
			1, 0, 0, 
			0, 1, 0, 
			0, 0, 1, 
			1, 1, 0});
	colorData.flip();

Rendering:

glBindBuffer(GL_ARRAY_BUFFER, vboVertexHandle);
	glVertexPointer(vertexSize, GL_FLOAT, 0, 0L);

	glBindBuffer(GL_ARRAY_BUFFER, vboColorHandle);
	glColorPointer(colorSize, GL_FLOAT, 0, 0L);
	
	glEnableClientState(GL_VERTEX_ARRAY);
	glEnableClientState(GL_COLOR_ARRAY);
	glDrawArrays(GL_QUADS, 0, amountOfVertices);
	glDisableClientState(GL_VERTEX_ARRAY);
	glDisableClientState(GL_COLOR_ARRAY);

I think that's all the relevant code you guys may need.


This is what the above code produces:

[Kai]

glOrtho does not allow any differences of left-right, top-bottom or near-far to be zero.
Therefore your current invocation of glOrtho is likely to generate a GL_INVALID_VALUE (see: https://www.opengl.org/sdk/docs/man2/xhtml/glOrtho.xml) and have no effect.
Just use as near = -1 and as far = +1 for example, and of course update your VBO to not use 0.0 and -1.0 but those pixel coordinates in [0..width] and [0..height]. Then it should work. It does for me at least.

[shadowstryker10]

I want to say I'm an idiot for not fixing this myself, but I had no idea that was even a thing. The reason I couldn't get it to work when I used -1 and 1 for the near/far values is because I never thought to convert the vertex data back into pixel coordinates. Thank you so much!