3D graphics questions that do not deserve their own thread (OpenGL / Dx10)

The Something Awful Forums > Discussion > Serious Hardware/Software Crap > The Cavern of COBOL > 3D graphics questions that do not deserve their own thread (OpenGL / Dx10)

newsomnuke: Feb 25, 2007

What does GL do when you try to upload a non-pow2 texture, without using the non-pow2 extension? When I do this, it works just as a pow-2 texture does, but:
(a) Does it upscale the texture to pow-2 internally, or leave it as it is
(b) Is the behaviour in a) dependent on GL version or anything else?
(c) Is there a way to get the width/height of an uploaded texture?

# ¿ Oct 2, 2008 09:51

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# ¿ Apr 29, 2024 14:08

newsomnuke: Feb 25, 2007

I presume that it also runs in plain debug mode, rather than only in the debugger? If this is the case, then it could be a whole number of things. My money's on uninitialised variables - see this page for more info.

# ¿ Oct 2, 2008 15:16

newsomnuke: Feb 25, 2007

How reliable are non-pow2 textures in OpenGL? They've been promoted to the core spec and I've never had any problem with them, but I've only had a very limited range of cards to test on (all nvidia). I've just come back to graphics coding after a pretty lengthy absence - are they still slow, or is the speed difference negligible?

# ¿ Dec 15, 2008 11:15

newsomnuke: Feb 25, 2007

Ok, that's a bit more drastic than I was expecting, and pretty conclusive. I was actually only considering using one for a full-screen overlay (ie using one 1024x768 texture) because using a 1024x1024 is causing slight but noticeable scaling artifacts. I don't think this is going to impact performance - I'm more worried that drivers (especially ATI's) will be dodgy and give me the old white texture routine.

# ¿ Dec 15, 2008 12:24

newsomnuke: Feb 25, 2007

OneEightHundred posted:

As far as I know, rectangle textures (see: ARB_texture_rectangle) give good speed on all hardware, you just have to deal with the fact that the coordinates aren't normalized and you can't mipmap them.

I've gone for this, thanks. I'm only using a small number of textures (less than 5), so I doubt performance will be a problem, but I've created a fallback just in case.

# ¿ Dec 16, 2008 13:25

newsomnuke: Feb 25, 2007

This is a bit of a ridiculous question because it seems so basic, but: I can't get smooth scrolling in OpenGL (using ortho projection). It seems to be because the floating point coords are getting rounded down (which makes sense) and I wouldn't have thought it would be noticeable at 60 fps, but it is. When I use integer coords, everything is fine.

# ¿ Jan 20, 2010 20:51

newsomnuke: Feb 25, 2007

Alcool Tue posted:

From my limited perspective on General Programming, properly declared float values aren't going to round themselves down unless you're turning them into ints OR you're running math with both ints and floats as values, which could either truncate your floats or add a .0 to your ints depending on some poo poo.

The rounding occurs when the positions are rasterised to screen, which is a set of discrete pixels.

# ¿ Jan 21, 2010 15:23

newsomnuke: Feb 25, 2007

What's up with this vertex shader?

code:

void main(void)
{
	vec4 pos = vec4(gl_Vertex);
	pos.w = 1;

	gl_Position = gl_ModelViewProjectionMatrix * pos;
}

It only works when I set vertices' 'w' coordinate to 1 before sending them to the GPU, for instance:

code:

for (size_t i = 0; i < vertSize; i += 4)
{
	verts[i + 0] = x;
	verts[i + 1] = y;
	verts[i + 2] = z;
	verts[i + 3] = distance; // only works if 'distance' is 1
}

...
glBufferDataARB(GL_ARRAY_BUFFER_ARB, vertSize * sizeof(GLfloat), verts, GL_STATIC_DRAW_ARB);
...
glBindBufferARB(GL_ARRAY_BUFFER_ARB, vertexId);
glVertexPointer(4, GL_FLOAT, 0, 0);
...
glDrawElements(GL_TRIANGLES, numFaces * 3, GL_UNSIGNED_SHORT, 0);

The vertices end up on screen, run through the fragment shader properly, just their positions are completely wrong. Why isn't the 'w' component being reset properly?

# ¿ May 16, 2010 00:04

newsomnuke: Feb 25, 2007

PDP-1 posted:

The w component of your vector should pretty much always be 1.

I know, which is why I reset it to 1 in the shader before applying the transform. But it doesn't seem to work!

edit: I'm using the 'w' component to store extra information which I use in the vertex shader, if you were wondering.

# ¿ May 16, 2010 02:19

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# ¿ Apr 29, 2024 14:08

newsomnuke: Feb 25, 2007

edit: ok, it's working. Turns out the problem was actually in the fragment shader where I was doing something with gl_FrontColor which I shouldn't have been doing.

newsomnuke fucked around with this message at 13:15 on May 16, 2010

# ¿ May 16, 2010 12:28

The Something Awful Forums > Discussion > Serious Hardware/Software Crap > The Cavern of COBOL > 3D graphics questions that do not deserve their own thread (OpenGL / Dx10)