OpenGL draw in SPRenderTexture

md.stage

I would like to draw OpenGL directly in a SPRenderTexture.
I saw that it's possible to do that while creating a new texture (http://wiki.sparrow-framework.org/manual/dynamic_textures).

But is there a way to draw in the SPRenderTexture directly? Or the only way is to create a new texture, then draw in the SPRenderTexture a SPImage created with this new one ?

Daniel

In theory, you could execute all kinds of OpenGL code in the drawBundled method, like this:

[renderTexture drawBundled:^
 {
    // ...
 }];

In that callback, OpenGL is set up correctly to render into the texture.

On the other hand, maybe what you're really trying to achieve is creating a custom display object altogether. That's described in this tutorial. Any object that is created that way can also be drawn into a render texture, of course.

I hope that helps!

humble

Hi. This drawBundle looks very interesting I think. Are there any examples of drawing a simple line in there? I also would like to be able to draw a circle and part of a circle.

I have tested some different small snippets of open gl code but they all seem to crash on the draw call, with a bad access.

Thanks

ERik

Daniel

The problem with that method is that it's quite an effort to actually set up all required OpenGL stuff to draw anything. The amount of set-up code has significantly grown with OpenGL ES 2 (vs. 1.x).

So you'd probably be better off with a custom display object, as in the link I posted above. You should be able to modify that code to create a circle (i.e. the polygon code with a high edge count) or a part of a circle.

Alternatively, remember that you can use Apple's Core Graphics, too, using the good-old "[SPTexture initWithWidth:height:draw]" method.

humble

Cool thanks, I will try that. I use the old SPTexture way now, but it is quite heavy on the cpu when redrawing every frame.

Cheers

ERik

humble

Until I learn about open gl, for my audio buffer line plots I used the drawBundle and a quad rotating it and stuff. It Seems to work ok for my 1 pixel height, going above that though makes not so smooth lines. But the performance boost using this compared to the old SPTexture init is big.

Anyhoo, If there is a wish list for sparrow, for me it is lines and circles/circle parts. We'll see if I can get around to figuring it out..

Thanks again Daniel

ERik

Shilo

@Humble

I have never been fond of creating lines with OpenGL ES because of the jaggedness and non-rounded ends. I once created a line extension for Sparrow 1.X, but I wasn't happy with the results. With OpenGL ES 2.0 and GLKit, you can multisample the entire stage to create smoother edges, but I don't think it would be possible to apply multisample on only one or more specific objects. I prefer not to use multisampling because it has a major performance hit.

I haven't had the need to create lines with Sparrow yet, but I much prefer to use Core Graphics strictly because of the quality of the lines. As you know, the overhead is much worse, and I won't even imagine using Core Graphics if I needed to update the dimensions per frame. I did create a Sparrow 2.X Line Texture extension which draws a line into an SPTexture via Core Graphics.

As far as circles, I have created Sparrow 1.X Circle extension and Sparrow 1.X Polygon extension. I suggest using a polygon class to create circles, as a circle is just a polygon with many edges. I also created a Sparrow 2.X Polygon & Polygon Image extension which is based on Daniel's wonderful Sparrow 2.X Polygon Sample and his Sparrow 2.X Polygon Texture Sample.

That's the end of the array of links!

humble

Cheers Shilo, much apperciated. I think at the moment I am in period of trying to push the cpu load down and see what is possible really.

Most circles I have I don't really update that often so I might be fine with the core graphics solution I have now. For the lines it is basically a xy plot with at the most, in landscape mode, 512 points. As you say about the smoothing, the core graphics lines look very good, but very slow. I am not sure if it the actual graphics that are the problem or if it is creating a new texture every time and adding it to an image.

Drawing quads into the drawBundled, is so much quicker, but doesn't look as nice.

ERik

Daniel

Thanks for putting together all those links, Shilo! 😃

There might be one alternative, ERik, even though it's a little hackish. Instead of using Quads, you could build up your lines using SPImages with a texture of the line PLUS a few transparent pixels around it. Then the bilinear filter (plus maybe mipmaps) will antialias your lines.

I recommended that once to a few Starling users, and it seemed to work well for them.

humble

Cool. Sounds like a neat little trick. So as I understand it the bilinear filter and mipmaps, not sure what that is, is done automatically? I don't need to do anything extra to add the filter? Will definitely try it.

Thanks

ERik

Shilo

I like Daniel's idea. I never tried it myself, but I always thought it would be a great solution.