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Q&A OpenGL: Pass a double vector from vertex shader to fragment shader

TL;DR: How to pass a interpolated double vector, such as a dvec2, from the vertex shader to the fragment shader? I have a vertex shader. In this the output variable out vec2 uv; is set. And i have...

1 answer  ·  posted 1y ago by H_H‭  ·  last activity 1y ago by H_H‭

Question glsl OpenGL
#2: Post edited by user avatar H_H‭ · 2023-08-22T16:48:53Z (about 1 year ago)
Add description and image to explain why `float` isn't precise enough.
  • TL;DR: How to pass a interpolated `double` vector, such as a `dvec2`, from the vertex shader to the fragment shader?
  • I have a vertex shader. In this the output variable `out vec2 uv;` is set. And i have a fragment shader, in this the (intperpolated) input variable `in vec2 uv;` is expected. This works, and the relevant shader parts looks like this:
  • Vertex shader:
  • ```
  • #version 400
  • out vec2 uv;
  • ...
  • void main()
  • {
  • uv = calculateUv();
  • ...
  • }
  • ```
  • Fragment shader:
  • ```
  • #version 400
  • in vec2 uv;
  • ...
  • void main()
  • {
  • doSomething(uv);
  • ...
  • }
  • ```
  • However, this uses only `float` or 32 bit precision. When i change it to `double` precision, by using `dvec2` instead of `vec2`, it no longer works and i get a
  • > error C7570: 64 bit input 'uv' should be flat
  • error. I can set `uv` to `flat`, but then it is no longer interpolated and it doesn't work as expected (the `uv` value is the same for all `fragments` on a face, which is not what i want). Non-working shaders:
  • Vertex shader:
  • ```
  • #version 400
  • out dvec2 uv;
  • ...
  • void main()
  • {
  • uv = calculateUv();
  • ...
  • }
  • ```
  • Fragment shader:
  • ```
  • #version 400
  • in dvec2 uv;
  • ...
  • void main()
  • {
  • doSomething(uv);
  • ...
  • }
  • ```
  • It isn't a problem of not accepting double in general, inside the shader i can use `double` based types such `dvec2` without any problem as long as i don't want to pass it to a other shader.
  • Any idea how to pass a `dvec2`? Or any workaround?
  • TL;DR: How to pass a interpolated `double` vector, such as a `dvec2`, from the vertex shader to the fragment shader?
  • I have a vertex shader. In this the output variable `out vec2 uv;` is set. And i have a fragment shader, in this the (intperpolated) input variable `in vec2 uv;` is expected. This works, and the relevant shader parts looks like this:
  • Vertex shader:
  • ```
  • #version 400
  • out vec2 uv;
  • ...
  • void main()
  • {
  • uv = calculateUv();
  • ...
  • }
  • ```
  • Fragment shader:
  • ```
  • #version 400
  • in vec2 uv;
  • ...
  • void main()
  • {
  • doSomething(uv);
  • ...
  • }
  • ```
  • However, this uses only `float` or 32 bit precision. When i change it to `double` precision, by using `dvec2` instead of `vec2`, it no longer works and i get a
  • > error C7570: 64 bit input 'uv' should be flat
  • error. I can set `uv` to `flat`, but then it is no longer interpolated and it doesn't work as expected (the `uv` value is the same for all `fragments` on a face, which is not what i want). Non-working shaders:
  • Vertex shader:
  • ```
  • #version 400
  • out dvec2 uv;
  • ...
  • void main()
  • {
  • uv = calculateUv();
  • ...
  • }
  • ```
  • Fragment shader:
  • ```
  • #version 400
  • in dvec2 uv;
  • ...
  • void main()
  • {
  • doSomething(uv);
  • ...
  • }
  • ```
  • It isn't a problem of not accepting double in general, inside the shader i can use `double` based types such `dvec2` without any problem as long as i don't want to pass it to a other shader.
  • Why `double` precession is needed: I draw a fractal and want to zoom. This is possible by changing the `uv`-coordinates but at a high zoom level, there are big artefacts from big, pixel-like, regions on the screen having the same `uv` value.![artefacts](https://software.codidact.com/uploads/lw5jy3pkcta336xi14ehwhshuris)
  • Any idea how to pass a `dvec2`? Or any workaround?
#1: Initial revision by user avatar H_H‭ · 2023-08-22T16:37:55Z (about 1 year ago)
OpenGL: Pass a double vector from vertex shader to fragment shader
TL;DR: How to pass a interpolated `double` vector, such as a `dvec2`, from the vertex shader to the fragment shader?

I have a vertex shader. In this the output variable `out vec2 uv;` is set. And i have a fragment shader, in this the (intperpolated) input variable `in vec2 uv;` is expected. This works, and the relevant shader parts looks like this:

Vertex shader:
```
#version 400

out vec2 uv;

...

void main()
{
  uv = calculateUv();
  ...
}

```

Fragment shader:
```
#version 400

in vec2 uv;

...

void main()
{
  doSomething(uv);
  ...
}

```

However, this uses only `float` or 32 bit precision. When i change it to `double` precision, by using `dvec2` instead of `vec2`, it no longer works and i get a 

> error C7570: 64 bit input 'uv' should be flat


 error. I can set `uv` to `flat`, but then it is no longer interpolated and it doesn't work as expected (the `uv` value is the same for all `fragments` on a face, which is not what i want). Non-working shaders:

Vertex shader:
```
#version 400

out dvec2 uv;

...

void main()
{
  uv = calculateUv();
  ...
}

```

Fragment shader:
```
#version 400

in dvec2 uv;

...

void main()
{
  doSomething(uv);
  ...
}

```

It isn't a problem of not accepting double in general, inside the shader i can use `double` based types such `dvec2` without any problem as long as i don't want to pass it to a other shader.

Any idea how to pass a `dvec2`? Or any workaround?