how to make a RGBA image fade away?

Member

Posts: 321
Joined: 2004.10

Post: #1

Nov 13, 2006 — 08:58 AM

I should probably know this, but i've got an RGBA image of 128x128 texels
and I just want the entire thing to fade away slowly until it is invisible?

glColor4x( r, g , b, alpha); is only for geometrical drawings and not for textures? right?

Sorry if this is a stupid question.

ThemsAllTook

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Posts: 1,552
Joined: 2003.10

Post: #2

Nov 13, 2006 — 09:00 AM

glColor works with textures.

NYGhost

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Posts: 157
Joined: 2002.12

Post: #3

Nov 13, 2006 — 09:58 AM

Code:

glEnable(GL_BLEND);

glBlendFunc(GL_DST_COLOR, GL_ONE_MINUS_SRC_ALPHA);

glBindTexture(GL_TEXTURE_2D, texid);

glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);

glColor4f(r, g, b, a);

if(a<1.0) a+=0.05;

Draw();

or something like that.

akb825

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Posts: 1,140
Joined: 2005.07

Post: #4

Nov 13, 2006 — 11:15 AM

Note that the calls to glEnable, glBlendFunc, and glTexEnvi only need to be called once. (just make sure the texture is bound when you call glTexEnvi, though)

WhatMeWorry

Member

Posts: 321
Joined: 2004.10

Post: #5

Nov 13, 2006 — 01:33 PM

Thanks.

Oops, I had commented out my glTexEnv(..) command. However, with that said,
how does the alpha of the glColor() command interact with the alpha bytes in the
RGBA texture? Does the glColor() override everything in the texture?

OneSadCookie

Luminary

Posts: 5,125
Joined: 2002.04

Post: #6

Nov 13, 2006 — 01:36 PM

It depends what you have set for TexEnv... MODULATE means "multiply". Read the man pages.

WhatMeWorry

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Posts: 321
Joined: 2004.10

Post: #7

Nov 13, 2006 — 06:34 PM

I read the man pages; it's the understanding that eludes me

akb825

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Posts: 1,140
Joined: 2005.07

Post: #8

Nov 13, 2006 — 07:58 PM

With GL_MODULATE, it multiplies the color values of the texture with the color values of the fragment. So if the color is {1, 1, 1, 1}, then it will be the exact same color as the texture. If you adjust the value of the alpha, then it will multiply the alpha of the image. Once it reaches 0, the image will be transparent.

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