CODEWITHSUNDEEP
openglglsl
Guillaume Magniadas
Guillaume Magniadas

Reputation: 176

Passing only 1 float in a sampler1D

I have multiple mesh that I want to draw in a glDrawElementsInstancedbut I want all the vertices to all have a different height so to do this I'm trying to pass the height by a sampler1D.

This is how I create the texture :

    glGenTextures(1, &meshHeightTexId_);
    glBindTexture(GL_TEXTURE_1D, meshHeightTexId_);

    glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);

    // meshHeight_.size() = meshNumber_*meshSize_
    glTexImage1D(GL_TEXTURE_1D, 0, GL_RED, meshNumber_*meshSize_, 0, GL_RED, GL_FLOAT, meshHeight_.data());

    glBindTexture(GL_TEXTURE_1D, 0);

(meshNumber_ is the numbers of mesh, meshSize_ is the number of vertices is contain and meshHeight_ is a float vector containing all the height data)

The call I do before the draw :

    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_1D, meshHeightTexId_);

And in the shader I gather the value like this :

int index = gl_InstanceID * meshSize + gl_VertexID;
vec4 tempo = texture(heightData, index);
float height = tempo.r;

(heightData is the name of the sampler1D I use and meshSize is an uniform int containing the number of vertices in a mesh)

Then I use the height as the y value of the vertice.

But by doing this it look like I only get height equal to 0 (Exept 1 in an angle for no reason).

I may doing something wrong at the initialization of the texture..

And also if you have a better idea than passing the height of meshes by texture I would take it.

Upvotes: 2

Views: 246

Answers (1)

Yakov Galka
Yakov Galka

Reputation: 72479

Just like GL_TEXTURE_2D, GL_TEXTURE_1D uses normalized texture coordinates. Since you set GL_CLAMP_TO_EDGE all values beyond [0, 1] will be clamped to that interval, so you get only the first and the last height value.

The function you're looking for is texelFetch:

vec4 tempo = texelFetch(heightData, index, 0);

Alternatively you can create a UBO and read the data from an array within.

Upvotes: 2

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