# OpenGL ARB Vertex Program: Reversing Tex Coords?

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I'm working on a vertex program for water, and what I want to do is have ripples flowing in opposite directions. I have the texture coordinates flowing in one direction by modifying the tex coords outside of the fragment program using standard OpenGL calls, and I figured I could simply multiply fragment.texcoord[1] by a negative value and make it flow the other direction. Apparently that isn't the case, or I'm doing something wrong. I can multiply it by different values and change the scale, but if I try to use negative numbers, the flow continues in the same direction as when they were positive. I've tried negating each component individually as well as various combinations, but nothing seems to work. Is my logic wrong, or can this simply not be done?

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I don't get what you're trying to do but try 1.0-fragment.texcoord[1]. Maybe that's what you want.

perhaps a clearer explanation would help me out...

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Ok, it looks like it wasn't doing what I thought it was doing.

Let me show some screenshots to better explain. I have a reflection texture that I'm distorting. I changed the distortion texture to be just an arrow, so you can see what it's doing.

http://www.planetquake.com/digitalpaint/images/devel/refl_distort_arrows.jpg
The texture is "flowing" in the direction the arrow points.

This is what happens when I scale it by 10:
http://www.planetquake.com/digitalpaint/images/devel/refl_distort_arrowsx10.jpg
Now the arrows are smaller, as one would expect. But then, when I scale it by -10, I get this:
http://www.planetquake.com/digitalpaint/images/devel/refl_distort_arrowsx-10.jpg
The texture is flipped, as you would expect, but it still flows in the same direction (not the direction the arrows are pointing).

Soooo.... my logic is just wrong. How would I get it to flow in the opposite direction without adding another texture unit with a new set of coords?

Here's the program, by the way:
!!ARBfp1.0PARAM half = { 0.5, 0.5, 0.5, 0.5 };PARAM inv = { -1.0, 1.0, 1.0, 1.0 };PARAM scaleFactor = { 4.0, 4.0, 4.0, 4.0 };PARAM testScale = { -10.0, -10.0, 1.0, 1.0 };TEMP distortColor;TEMP distortColor2;TEMP texcoord1Inv;TEMP distortCoord;#SUB texcoord1Inv, half, fragment.texcoord[1];MUL texcoord1Inv, fragment.texcoord[1], testScale;#MOV texcoord1Inv, fragment.texcoord[1];TXP distortColor, fragment.texcoord[1], texture[1], 2D;TXP distortColor2, texcoord1Inv, texture[1], 2D;#ADD distortColor, distortColor, distortColor2;MOV distortColor, distortColor2;SUB distortColor, distortColor, half;MUL distortColor, distortColor, scaleFactor;ADD distortCoord, distortColor, fragment.texcoord;TXP result.color, distortCoord, texture, 2D;END

Don't mind the mess -- lots of testing. Half the code doesn't do anything. This is the first time I've touched fragment programs.

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I figured out how to do it -- just passed an offset parameter. Sorry, I'm new to fragment programs. A whole whopping 2 days of experience. ;)

I'm making good headway, though, but I've run into something that baffles me. Currently I'm using 2 textures. One that reflects and one that distorts. I bound a 3rd texture -- I haven't enabled it or changed any of the fragment program code at all. I just bound it. Yet, somehow, it's changing the effect of the fragment program.

Before (2 textures bound):

After (3 textures bound, 3rd completely unused):

(the distortion is considerably more subtle)

I don't get that. Why should binding a 3rd texture have any effect whatsoever?

Edit: Nevermind. I'm not sure what I did exactly, but I fixed it. Something with the way Q2 handles multitexturing -- it was setting it to the wrong texture unit.

[Edited by - jitspoe on June 15, 2005 12:35:41 PM]

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