Forums - Problem with discard statement in fragment shader on Adreno205(Android 2.3.4)

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Problem with discard statement in fragment shader on Adreno205(Android 2.3.4)
Kazuhiko_Kobayashi
Join Date: 14 Feb 12
Posts: 9
Posted: Tue, 2012-02-14 11:59
Hi,
My application works fine on Adreno200, but It doesn't work on Adreno205.Android OS freezes.
I investigated the cause and I discovered it.
My shader source:
   161     if(alpha < 0.1 /*m_AlphaDiscardThreshold*/){
   162         discard;
   163     }
I commented out line 161-163, it works fine on Adreno205.
Question:
Why discard doesn't work on Adreno205?
Test phone SHARP IS05(Android 2.3.4)
My application(free):
Thanks.
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Kazuhiko_Kobayashi
Join Date: 14 Feb 12
Posts: 9
Posted: Tue, 2012-02-14 17:01

This is a sample which works on Adreno200, but it doesn't work on Adreno205.

http://chototsumoushinp.dip.jp/miku/download/AndroidSample_tinyar-116-ad...

I removed discard statement in the fragment shader, it works on Adreno205.

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Kazuhiko_Kobayashi
Join Date: 14 Feb 12
Posts: 9
Posted: Sun, 2012-02-19 17:37

Hi,

This shader freezes on Adreno205.

precision mediump float;
varying vec2 vTexcoord;
uniform lowp sampler2D ColorMap;
void main()
{
    gl_FragColor= texture2D( ColorMap, vTexcoord );
    discard;
}

However, this shader doesn't freeze.

precision mediump float;
varying vec2 vTexcoord;
uniform lowp sampler2D ColorMap;
void main()
{
    lowp vec4  color= texture2D( ColorMap, vTexcoord );
    if( color.w < 0.7 ){
        discard;
    }
    gl_FragColor= color;
}

Thanks.

 

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Mark_Feldman Moderator
Join Date: 4 Jan 12
Posts: 61
Posted: Wed, 2012-02-22 16:00

In general we discourage the use of the discard statement as it is a very expensive operation.  You will have much better performing code by eliminating its use and rewriting the shader (for example setting alpha to 0 with alpha blending enabled).

 

(e.g.) http://stackoverflow.com/questions/8509051/is-discard-bad-for-program-pe...

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Kazuhiko_Kobayashi
Join Date: 14 Feb 12
Posts: 9
Posted: Thu, 2012-03-01 13:39

Hi,

I know that.

However, I need it because some models can't draw without it.

Thanks.

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