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Higher quality skybox?

Started by Last Attacker Jul 9, 2006 at 12:47 PM 7 replies 2.3k views

Original Post

Jul 9, 2006 at 12:47 PM

Hi. I have implemented a skybox in OpenGL which I have generated with Terragen. But it seems it doesn't matter where I get skybox images from I get a pretty low-res image. I use 512 x 512 24-bit TGA images. Here is a screenshot of the window with the skybox. Does anyone know what I should do to enhance its appearance? Thanks

ViLiO

Jul 9, 2006 at 12:53 PM

Are you using a linear filter or point filtering?

From the screenie it looks like point filtering (GL_NEAREST) so you could try using linear filtering (GL_LINEAR).

All the best,
ViLiO

Last Attacker

Jul 9, 2006 at 12:57 PM

Here is the filter source I use, my skybox textures are set on FILTER_TRILINEAR.

void SetFilterMode(const void *Data, GLsizei Width, GLsizei Height, FILTER_MODE FilterMode, PIXEL_FORMAT ColorMode){	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);		switch (FilterMode)	{	case FILTER_BILINEAR:		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST);		//glTexImage2D(GL_TEXTURE_2D, 0, 4, Width, Height, 0, ColorMode, GL_UNSIGNED_BYTE, Data);		glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);		gluBuild2DMipmaps(GL_TEXTURE_2D, 4, Width, Height, ColorMode, GL_UNSIGNED_BYTE, Data);		break;	case FILTER_TRILINEAR:		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);		//glTexImage2D(GL_TEXTURE_2D, 0, 4, Width, Height, 0, ColorMode, GL_UNSIGNED_BYTE, Data);		glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);		gluBuild2DMipmaps(GL_TEXTURE_2D, 4, Width, Height, ColorMode, GL_UNSIGNED_BYTE, Data);		break;	case FILTER_NONE:	default:	//If none or wrong filter mode, then assume FILTER_NONE		glPixelStorei(GL_UNPACK_ALIGNMENT, 1);		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);		glTexImage2D(GL_TEXTURE_2D, 0, 3, Width, Height, 0, ColorMode, GL_UNSIGNED_BYTE, Data);		}}

deathkrush

Jul 9, 2006 at 1:02 PM

You could try bypassing the mipmaps and always use the highest resolution image. It kind of doesn't make sense to use mipmaps with a skybox.

OrangyTang

Jul 9, 2006 at 1:06 PM

That looks rather like a Terragen render to me, unfortunately the rendering quality of Terragen isn't terribly good at times, and you seem to be suffering from lots of jaggies.

Try doing your terragen render at a much larger resolution (say, 2048x2048) then manually resizing that down to 512x512 in a good paint program. This will give you a quick and easy antialiasing of the edges.

Incidentally you don't need a triliner filter for skyboxes, you should have them set at the correct size so that mipmaps never get used. Regular bilinear should look just as good and be faster.

Edit: Ha! I hope your skybox textures are power-of-two sized (512x512, 256x128, etc.). Otherwise gluBuild2DMipmaps will do a (crappy) resize to the nearest power of two, which is going to make the resulting texture look horrible.

Last Attacker

Jul 9, 2006 at 1:07 PM

Ok, I'll try that.
Does my filter code look ok?

Last Attacker

Jul 9, 2006 at 1:27 PM

Thanks OrangyTang!
It looks much better.

EDIT: I made a 1280 x 968 image (the freeware version didn't allow more) and shrunk it with Paint Shop Pro 8 to 512 x 512 (boy it renders long [headshake]).
Then I used Bilinear filtering.

[Edited by - Last Attacker on July 9, 2006 1:27:31 PM]

Last Attacker

Jul 10, 2006 at 10:39 AM

Unfortunately when I rendered for different directions I saw that the Terragen free-limitation caused a problem. Since the largest image won't produce a power of 2 image, it caused that the left, right, top, bottom, front and back images doesn't properly fit.
But I used PSP's Soft image effect and made it a little bit blurry like this (on the first image with the terrible quality):

Atleast all edges fits and it looks better than the first one.

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