Databases
StackOverflow2013
Postsdbo
POOpenGL ES 2.0 texture2D bias/lod
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POOpenGL ES 2.0 texture2D bias/lod
    primarykey
    data
    text
    <p>I am using the OpenGL ES 2.0 GLSL functionality to manipulate images. What I want to achieve is to select a specific Level Of Detail (LOD) when fetching a sample from a texture from within a fragment shader. Apparently <code>texture2DLod()</code> is not supported for fragment shaders in OpenGL ES 2.0 (but there is an extension <a href="http://www.khronos.org/registry/gles/extensions/EXT/EXT_shader_texture_lod.txt" rel="nofollow noreferrer"><code>GL_EXT_shader_texture_lod</code></a> that can optionally provide it.)</p> <p>However, the default <code>texture2D()</code> function provides a third optional parameter bias. As far as I understand, this parameter is supposed to be an offset added to the current LOD.</p> <p>In my tests I'm drawing a quad the size of the screen and I'm magnifying a texture by scaling the sample coordinates. I've enabled mipmapping for the texture using GL_LINEAR_MIPMAP_LINEAR as a minification filter. The result when sampling with a non-zero bias parameter on the ARM Mali-400 GPU can be seen in the image below.</p> <p>ISTM that some pixels are using the minification filter while others are using the magnification filter.</p> <p>How is this controlled? And how do I determine the initial LOD when using bias? Can it be adjusted from the vertex shader?</p> <p>A related question is the following one:</p> <p><a href="https://stackoverflow.com/questions/7367606/how-does-a-glsl-sampler-determine-the-minification-and-thus-the-mipmap-level-o">How does a GLSL sampler determine the minification, and thus the mipmap level, of a texture?</a></p> <p><img src="https://i.stack.imgur.com/kBNTh.png" alt="texture2D with bias parameter on ARM Mali-400"></p> <p>Update: I noticed that if I sample the texture so that it covers the screen, then it seems to do the proper mipmap look-up (even though it is magnified.) Now, if I add a small offset to the sample coordinates, then I will begin to see the banding that is seen in the above image (which is magnified even more.) If I don't use the bias parameter I will not see any banding at all.</p>
    singulars
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PTQuestion
    1. USCommunity
    1. USMattias Andersson
    plurals
    1. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. VO
      singulars
      1. POOpenGL ES 2.0 texture2D bias/lod
      1. USweston
      1. VTFavorite
    2. VO
      singulars
      1. POOpenGL ES 2.0 texture2D bias/lod
      1. This table or related slice is empty.
      1. VTUpMod
    1. CODid you ever figure this one out? From a quick look at the GLSL 2 specs, texture2Dlod should be fully supported, alas my device falls back to a fully-black shader when using tex2dlod... did you get any workable results with the bias param at all?
      singulars
      1. POOpenGL ES 2.0 texture2D bias/lod
      1. USmetaleap
    2. CONever managed to programmatically fetch from a specific texture LOD level. My workaround was to create a texture atlas and manually render each LOD level.
      singulars
      1. POOpenGL ES 2.0 texture2D bias/lod
      1. USMattias Andersson
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload