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Colored triangle (using vertex colors) renders white #894

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vchelaru opened this issue Oct 20, 2012 · 10 comments
Closed

Colored triangle (using vertex colors) renders white #894

vchelaru opened this issue Oct 20, 2012 · 10 comments
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Android Android platform OpenGL OpenGL graphics backend Windows

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@vchelaru
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I have a simple-to-reproduce case where a simple triangle does not render properly. Here is the source code which can be pasted into a Game class to reproduce the error:

http://pastebin.com/HbW0PVif

This exact code in XNA 4 (on the PC) results in a triangle with the verts being red/green/yellow. On Android (specifically Motoroal Droid Razr) renders the triangle correctly for 1 frame. The next frame the triangle renders, but it renders white instead of colored. I suspect something is not being preserved in the states frame-to-frame; however in my investigation of the code it looks like we're using pixel shaders, which I'm not as familiar with in open GL - were it fixed function I may have been able to identify the issue.

Anyway, given the relatively easy repro steps I don't think it'll be hard for those more knowledgeable with OGL to figure out what's going on.
@bonesoul
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bonesoul commented Feb 7, 2013

I just tested this with 3.0 stable release, it still exists. Created a test project for it; http://dl.dropbox.com/u/197820/monogame/monogame-3.0-stable-issue894.rar

monogame-3 0-stable-issue-894-test

Also tested develop3d and still it also effects it.

monogame-develop3d-issue894

@vchelaru
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vchelaru commented Feb 7, 2013

Thanks for looking into this and reviving the issue. It's currently our main blocking issue on getting FlatRedBall on Android.

@bonesoul
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bonesoul commented Feb 7, 2013

I'll be taking further time to investigate it.

@lazlo-bonin
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I'm getting the same problem on Windows 8 Desktop (with OpenGL template).
Could you update the label?

@vchelaru
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Updated. raistlinthewiz - find anything?

@dbeals
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dbeals commented Sep 14, 2013

This is being caused by the BasicEffect class recomputing the shader index, which is changing the technique from BasicEffect to BasicEffect_NoFog. If I set the flag FogEnabled to true it works just fine (BasicEffect.OnApply(), BasicEffect.cs:472.)

Sadly I'm not sure how to actually correct this in the code.

@Chaosus
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Chaosus commented Mar 18, 2015

@tomspilman I think this issue should be closed(or revisited). The amount of work that should be done for fixing it is huge. The XNA shares one technique whereas MonoGame shares 32 technique within one BasicEffect. And as you look into
http://pastebin.com/HbW0PVif you could observe

foreach (var pass in _effect.Techniques[0].Passes)

is incorrect, there must be

foreach (var pass in _effect.CurrentTechnique.Passes)

@tomspilman
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is incorrect

Yeah... does XNA even allow rendering of passes that are outside the current technique? It seems dangerous and unnecessary really. Switch techniques if you need to switch techniques.

@Chaosus
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Chaosus commented Mar 18, 2015

The code above draws colored triangle correctly on XNA, but it is incorrect by nature.

@tomspilman
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Yeah... I say it is invalid even in XNA. It just happens to work.

alxwest pushed a commit to alxwest/MonoGame that referenced this issue May 3, 2024
@nkast
fix content builder CopyItems race condition (MonoGame#894)
c74d589
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@bonesoul @tomspilman @vchelaru @Chaosus @lazlo-bonin @dbeals