CODEWITHSUNDEEP
androidopengl-es3dtexturessprite
user2255673
user2255673

Reputation: 237

Android / Offscreen rendering to texture

I am making a 2D graphical app that will display planets. I say 2D because the majority of the app will be 2D. I however want to render some 3D objects into dynamic sprites offscreen (to a texture), with transparent (possibly translucent) areas, and subsequently render those rendered textures to the active screen as 2D textured quads. Rendering directly to the screen as 3D objects is not optimal in this case, because it would require me to implement some sort of 3D picking. I am not that advanced in math yet. Note also that the main screen render will be orthographic, while the offscreen render would be perspective.

How can I accomplish this (general idea, no need for specifics), and what would be the most efficient way to do this? Would this reduce support for a wide variety of devices? Also, if the 3D sprite renderings were constantly refreshed every frame (such as being rotated fine amounts) would that kill framerates with continuous unloading/reloading of texture to memory? I suppose that some scenes could have as many as 10 of these 3D offscreen sprites.

Thanks for the help

Upvotes: 3

Views: 2255

Answers (1)

Matic Oblak
Matic Oblak

Reputation: 16794

If you really must use the offscreen rendering just search for FBO(frame buffer object) and attach a texture to it, then use the texture in your main view as 2D. It is quite a straight forward procedure but might decrease the speed. You will probably not be able to do any multithreading on it so you should create just 1 FBO. Its dimensions will probably have to be a power of 2 so the resolution might be different then you wish. This procedure does not continually load/unload anything, the data is allocated when creating the texture and GL draws/reads directly from it. The largest drawback here will be the memory.. You will create as many as 10 of this textures just to draw on them and present once.

It might be very easy to place this objects on a specific place on your main buffer though: Make all the logic as if you would want to draw a full screen planet but use "viewport" method to place it to a specific part of the screen.

If those planet images will be updated only on user request (you don't want to draw them every frame) then I suggest you try to make a combination of both: Create a FBO with a texture of same size or larger then main view and draw all the planets to this single texture using "viewport" method. Then you can update any you want, just don't clear the buffer, rather draw a clear rect on the specific part of the buffer/texture. And keep drawing the whole texture to the main buffer.

Upvotes: 2

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