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Hello All,

I've tried to implement a 2D dynamic lighting algorithm based on filling triangles, unfortunately it would not perform well with the SLD_Renderer functions, and so I realized that using OpenGL (with which I have no experience) for drawing the triangles would be a possible solution.

Basically, what I would like to be able to do is: Keep using SDL for copying to and from SDL_Textures just as I have been working so far, and use OpenGL only to render triangles to an SDL_Texture which I also could copy from.

So.., It has been weeks now, reading and experimenting with OpenGL, and unfortunately I have not been able to mix SDL and OpenGL, here is basically the test I am stuck with:

* Initialized OpenGL with SDL (OpenGL SDL window, OpenGL context tied to the SDL window).
* Created an SDL_Renderer tied to the SDL window so that I could create SDL_Textures.
* Created an SDL_Texture that I filled with a color using the SDL_Renderer.
* Created the data buffers (VBOs and VAO) for a QUAD that fills the screen and the VUs that would texture the QUAD.
* I bond the SDL_Texture with SDL_GL_BindTexture.
* Run the shader program (vertex and fragment shaders) that is supposed that take the data and draw to the screen.

So well, it did not work, I don't even know if it is possible or what I am missing.

Lastly, just to be clear, I have been able to draw and fill the QUAD with colors using OpenGL rendering only, but I'm having a hard time with mixing SDL_Textures and Renderer with OpenGL.

Any help I could get I'll be so very thankful, I don't want to give up on my 2D Dynamic lighting.

Best Regards
Gabriel

From what I've read SDL basically uses the entire OpenGL state when you use the render api. You could have a look at the source and see how much SDL actually needs from the OpenGL state, but I've never read any guarantees about that from SDL's side. I could be wrong though. Maybe you can describe what exactly "did not work"? In what way did it not match your expectations?

On 11 May 2016 at 09:37, gabf83 wrote:

On 5/11/16, gabf83 wrote:


There have been previous threads on this and related topics, though
they are scattered and hard to find. Here is my attempt to organize
them.

On mixing OpenGL and the SDL 2D renderer, Gabriel Jacobo developed
this solution for integrating a GUI library called librocket.
http://mdqinc.com/blog/2013/01/integrating-librocket-with-sdl-2/
https://bugzilla.libsdl.org/show_bug.cgi?id=1138

There was a discussion/proposal of adding a batching API for
submitting quads to the 2D renderer.
https://forums.libsdl.org/viewtopic.php?p=48449&sid=cc802ffa803aa9e6614a9ee23ff476a2

Gabriel Jacobo also proposed a direct triangle rendering function
"SDL_RenderGeometry" to handle more arbitrary geometry submission to
the 2D renderer.
https://forums.libsdl.org/viewtopic.php?t=8850&sid=0e06d37272e22e0204ce68f8fb92c424


For your situation though, you might strongly consider using SDL_gpu
by Jonathan Dearborn. You can think of it as another alternative SDL
2D renderer (which happens to be built on top of OpenGL right now). It
tries to bridge that gap between keeping a lot of SDL's simpler/easier
semantics, while still giving you a lot more access to OpenGL
features. I think it has done a pretty good job striking that balance.
It provides APIs to pass an SDL_surface and load it as GPU_Image which
is very similar to an SDL_Texture. It provides GPU_Blit* functions
which are very similar to SDL_RenderCopy*. And SDL_gpu provides access
to GLSL shaders so you can load in your shaders.

I'm currently writing a couple of demos using it, including a dynamic
lighting system for 2D sprites using normal maps generated by popular
tools out there.

-Eric
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Hi

my experience so far is that *some* mixing between openGL and Renderer
is possible with some care. For instance you can render an SDL texture
and then render directly some openGL quads onscreen. For this to work
you need to reset things like shader programs at every frame.  However
I have never tried to use openGL to render directly onto and SDL
texture. This might be impossible at this point.  I hope that SDL can
evolve in this direction in the future.

S.

Le 11/05/2016 09:37, gabf83 a écrit :

Thanks for your replies. Fortunately, Gabriel Jacobo released a patch that provides the SDL Renderer with a Geometry Rendering function. I was able to patch SDL 2.0.0 and tested that it works and does exactly what I was looking for.

Interestingly, it appears that the trick is having the same OpenGL render context that SDL Render uses render whatever you want OpenGL to render for you.

Regards
Gabriel

interesting, coud you give the link to the patch ?


Le 30/05/2016 22:52, gabf83 a écrit :

Sure,

This is the link to the bug where the patch is:

http://bugzilla.libsdl.org/show_bug.cgi?id=1734

This is the post where it was shared:

https://forums.libsdl.org/viewtopic.php?t=8850&sid=0e06d37272e22e0204ce68f8fb92c424

Really hopping this officially makes it to SDL next releases.

Regards