How to replace a GLSL uniform array with a 1D texture

Question

I am trying to get Ardor3D's terrain system to work on SM3.0 hardware.

The current GLSL fragment shader uses a uniform vec2 array to pass an array of xy coordinates into the fragment shader.

As dynamic indexed uniform arrays only work on SM4.0+ hardware, to get it running on SM3.0 I need to replace it with a 1D float texture.

The current array looks like this: uniform vec2 sliceOffset[8];

and is accessed like this: vec2 offset = sliceOffset[int(unit)];

I am very experienced with OpenGL and GLSL so I am having some problems doing the conversion.

So far I have done this: Create a 1D texture - width = 8 - format = RGBA32F

Create a 1D buffer for the texture

width = 8 * 4 = 32 floats, or 32 * 4 = 32 bytes large
fill the float buffer like this:

[x0,y0,0,0,x1,y1,0,0,x2,y2,0,0,x3,y3,0,0,x4,y4,0,0,x5,y5,0,0,x6,y6,0,0,x7,y7,0,0]

Create a 1D sampler for the texture

min filter = nearest, no mip maps
mag filter = nearest
wrap mode = clamp to edge

In the GLSL I define the sampler as: uniform sampler1D sliceOffset;

And accesses it:

vec2 getSliceOffset(float unit)
{
 float texCoord = (unit * 2.0f + 1.0f) / (2.0f * 8.0f);
 vec2 offset = texture1D(sliceOffset, texCoord);
 return offset;
}

But it is broken.

What am I doing wrong?

Bahbar Bahbar · Accepted Answer · 2010-12-04T08:12:22

Everything you're showing looks right. "It is broken" is not very descriptive though. What are the symptoms ?

Some things that you don't show that may be wrong:

2 samplers using the same texture unit.
type issues in the texture data (although if you're experienced, I doubt it)

One additional thing you could try: use a texture2d instead, with just height=1. DX does not require 1d texture support, so depending on hardware, the opengl support for it might be emulated. You can try to stay away from such emulation.

How to replace a GLSL uniform array with a 1D texture

2 Answers