OpenGL / GLSL - Using buffer objects for uniform array values

Question

My (fragment) shader has a uniform array containing 12 structs:

struct LightSource
{
    vec3 position;
    vec4 color;
    float dist;
};
uniform LightSource lightSources[12];

In my program I have 12 buffer objects that each contain the data for one light source. (They need to be seperate buffers.)

How can I bind these buffers to their respective position inside the shader?

I'm not even sure how to retrieve the location of the array.

glGetUniformLocation(program,"lightSources");
glGetUniformLocation(program,"lightSources[0]");

These run without invoking an error, but the location is definitely wrong(4294967295). (The array is being used inside the shader, so I don't think it's being optimized out)

You are aware that glGetUniformLocation returns a signed number, right? That number is way too large for GLint (32-bit signed integer) to store. You are almost certainly misinterpreting the sign of that number. — Andon M. Coleman
– Andon M. Coleman, Commented Dec 27, 2013 at 18:37

ilw · Accepted Answer · 2024-04-20 17:06:17Z

4

As glGetUniformLocation docs say:

name must be an active uniform variable name in program that is not a structure, an array of structures, or a subcomponent of a vector or a matrix.

...

Uniform variables that are structures or arrays of structures may be queried by calling glGetUniformLocation for each field within the structure.

So, you can only query one field at a time. Like this:

glGetUniformLocation(program,"lightSources[0].position")
glGetUniformLocation(program,"lightSources[0].color")
glGetUniformLocation(program,"lightSources[0].dist")

Hope it helps.

###Edit:### You can make your life easier (at a cost of old hardware/drivers compatibility) by using Interface Blocks, Uniform Buffer Objects and glGetUniformBlockIndex. This will be more like DirectX constant buffers. Required hardware/drivers support for that: either OpenglGL 3.1 core or ARB_uniform_buffer_object extension.

edited Apr 20, 2024 at 17:06

ilw

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answered Dec 27, 2013 at 16:32

Drop

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3 Comments

zero298 Over a year ago

Yeah, I found this out a while ago and ended up using a string mangling loop to encapsulate having to manually set each uniform myself.

Silverlan Over a year ago

So I assume I'll have to use glBindBufferRange on each buffer and set each field manually? I was hoping there was a more direct way of doing it, but I guess it'll have to do.

Drop Over a year ago

@Silverlan yes, each field manually. I've edited answer to add some info about how to make it easier.

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