SDL2 and OpenGL functions with two windows - opengl

I am trying to make one application with two windows with SDL2. To make draw process faster and capable to run 3d animations I am using OpenGL. But when I open second window, how can I said to OpenGL (gl functions) to draw in second window?
I searched into libsdl wiki but cant find anything.

You are looking for the SDL_GL_MakeCurrent function.
Use this function to set up an OpenGL context for rendering into an OpenGL window.
Example:
SDL_GL_MakeCurrent(window, gl_context);
// OpenGL functions will draw to window
// ...
SDL_GL_MakeCurrent(window2, gl_context);
// OpenGL functions will draw to window2

Related

render a qt overlay window over opengl child window

I am looking for some information about rendering child windows in specific about how OpenGL interop with GDI. The problem that I have is that I have basically is that I have two windows, first, the main windows are created in qt, and inside of qt, a child window is hosted that leverages an OpenGL renderer.
Now what I wanted to do is to host an overlay on top of my OpenGL window, so I use that to overlay the OpenGL window. The problem that I am having is that when I render with OpenGL, the OpenGL generated graphics seem to obscure the graphics area including and effectively undo the graphics composited by qt.
In the image below the blue area is the qt overlay, in that picture I'm using GDI (BeginPaint/EndPaint) so and the windows seem to interact fine. That is, window order seems correct, the client region is correct. The moment I start to render with Opengl the blue area gets replaced with whatever OpenGL renders.
What I did I basically created to create the overlay I created a second frameless, topmost QMainWindow, and once the platform HWND was initialized I reparent it. Basically I change the new windows parent to be the same parent of my OpenGL window.
What I believed this would do is that the every window, gets drawn separately and the desktop composition manager would make the final composition and basically avoiding the infamous airspace problem as documented by Microsoft in their WPF framework.
What I would like to know is what could cause these issues? At this point, I lack understanding why once i render with OpenGL the pixels by qt overlay are obscured, even though windows hierarchy should say make them composited. What could I do to accomplish what I want?
Mixing OpenGL and GDI drawing on a shared drawable (that also includes sibling / childwindows without the CS_OWNDC windowclass style flag) never was supported. That's not something about Qt, but simply how OpenGL and GDI interact.
But the more important issue is: Why the hell aren't you using the OpenGL support built right into Qt in the first place? Ever since Qt-5 – if available – uses OpenGL to draw everything (all the UI elements). Qt-5 makes it trivial to mix Qt stuff and OpenGL drawing.

Combining GLX (OpenGL) and X11 graphics

I have to write an application on Linux using X11 for the interface (in C++). The application uses GLX to render some openGL graphics, but I also need to write some custom UI for this app within the same window.
When I create window I created a GC and a GLX context. Ideally I'd need to "draw" the openGL into a region of the window (say the left part) and the draw the UI on the side of the GL viewport.
How can I do that?
how can i combine GLX and GC drawing calls, such as XDrawString for example.
what would be the best way for me to create a layout within the same window, reserving a region of the window in which I draw the GL content, and having another region of the window in which I draw the UI using X calls. Do I need to create sub-windows for that?
I actually found a useful answer here:
Create GLX context in specific region of a window
The idea is to spawn a sub-window from the current window and draw the GL content to it.
I'd suggest to use BindTexImage extension, draw your X11 (via core / xrender / whatever ) commands to offscreen pixmap and then later composite it as a texture.

Is it possible to draw outside the client window using OpenGL

Just like to add a bit question similar to this link. Is there anyway I could do to draw outside the client window using OpenGL without any native commands to be used? or is this beyond OpenGL previleges?
Other ways I could think of is to draw a sub window and remove the built in borders and button on it, then draw what I wanted there?

Using a SDL window with OpenGL the other way around

I just recently changed all rendering in my application/game from SDL to OpenGL. I still use SDL for keyboard input, loading images and creating the window.
But since i only render in OpenGL do you think that i should change the window to a OpenGL initialized window instead of a SDL window. The header i use for OpenGL functions at the moment is "SDL_opengl.h". Does that affect things?
What are the advantages and disadvantages if i do this? Right now it feels like it's the logical "next step" since i got rid of all other SDL rendering code.
Just keep on using SDL for input and window management.
There's no provision for either in the OpenGL spec so there's really no such thing as an "OpenGL initialized window".
As genpfault said, you should keep using SDL for your window initialization. It's more clean and portable than OS-specific methods of initializing a window for OpenGL rendering.
I would also recommend switching from SDL_opengl.h to SDL.h and gl.h; the definitions in SDL_opengl.h aren't necessary for basic window management, and they conflict with the definitions in other OpenGL libraries like GLEW (which you may want to use later for pixel shaders and framebuffers).

How to get X to render to an OpenGL texture?

I am trying to write a compositor, like Compiz, but with different graphical effects. I am stuck at the first step, though, which is that I can't find how to get X to render windows to a texture instead of to the framebuffer. Any advice on where to start?
X11 composition goes like following.
you redirect windows into a offscreen area. The Composite extension has the functions for this
you use the Damage extension to find out which windows did change their contents
in the compositor you use the GLX_EXT_texture_from_pixmap extension to submit each windows' contents into corresponding OpenGL textures.
you draw the textures into a composition layer window; the Composite extension provides you with a special screen layer, between the regular window layer and the screensaver layer in which to create the window composition is taking place in.