[Interest] Qt Quick Scene Graph, texture questions, Qt 5.2.0

[Gunnar Sletta]

On 20 Jan 2014, at 11:54, Ola Røer Thorsen <ola at silentwings.no> wrote:

> Hi, I've got 3 questions about texture use in the Qt Quick scene graph:
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> 1.
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> In general it's recommended in OpenGL to use power-of-two-sized textures whenever possible, for performance resons. Does the Qt Quick scenegraph deal with this in any way, or is it up to the user to use properly sized images whenever possible? 
> 
> By "deal with this", it could be that the scenegraph adds some padding to fit an image within the closest larger power-of-two size, at the cost of wasting some memory. 

The scene graph uses the images it gets in the size it gets them in. However, it does try to get them into an atlas which is power-of-two.

> 
> 2. 
> 
> I've tried the option to visualize which images are put in a texture atlas (QSG_ATLAS_OVERLAY). In my application, that has a lot of smaller icon images (128x128 mostly), just about half of them are put in the atlas. Is there just a single texture atlas implemented, or are there several of them? My impression is that there is only one, and it gets filled up rather quickly. 

There is only one, but you can make it larger on your platform by changing QSG_ATLAS_WIDTH and QSG_ATLAS_HEIGHT to GL_MAX_TEXTURE_SIZE if you want a bigger one.

> 
> 3.
> 
> How does Qt Quick deal with trying to show an image that is larger than the maximum texture size supported on the targeted GPU? Does it tile several textures internally? 

It doesn't deal with this and the result will be a black square.

> 
> Cheers,
> Ola
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