The limit of "for" in shader?
Author
Hi all:
I try to do computation in shader.
First, I do a FBO object and attatch 4 color + 1 depth texture
my sizes are 725 x 401
Second, I do a simple loop in fragment .
int b =0;
for(int i = 0 ; i<n ;i++)
b++;
gl_FragColor = vec4(b,b,b,1.0);
if n is 280 , I got 24
n is 270 14
n is 260 4
n 250 250 is right!
Everyone konw what's wrong with me?
Please tell me some tips or relative site.
Thank you very much!
Where are you taking the output value from?
It obviously clamps the value to 256 and wraps up back again, 280-256=24,270-256=14 etc..
Either way, unless you're using floating point target, you shouldn't be storing that big numbers!
ch.
It obviously clamps the value to 256 and wraps up back again, 280-256=24,270-256=14 etc..
Either way, unless you're using floating point target, you shouldn't be storing that big numbers!
ch.
instead of
try
Quote:Original post by ARB1130
gl_FragColor = vec4(b,b,b,1.0);
try
gl_FragColor = frac(vec4(b,b,b,1.0)*vec4(1,256,65536,1));
Author
Quote:Original post by rapso
instead ofQuote:Original post by ARB1130
gl_FragColor = vec4(b,b,b,1.0);
try
gl_FragColor = frac(vec4(b,b,b,1.0)*vec4(1,256,65536,1));
Thanks your responds!
Your approach is packing a float into a texture.
I got 0 ^_^"
And I got the values by glReadPixels.
Author
Quote:Original post by christian h
Where are you taking the output value from?
It obviously clamps the value to 256 and wraps up back again, 280-256=24,270-256=14 etc..
Either way, unless you're using floating point target, you shouldn't be storing that big numbers!
ch.
Thanks to your idea! ^_^ 256
Yes, I use the GL_RGBA32F_ARB and GL_TEXTURE_RECTANGLE_NV
Author
Quote:Original post by ARB1130
Hi all:
I try to do computation in shader.
First, I do a FBO object and attatch 4 color + 1 depth texture
my sizes are 725 x 401
Second, I do a simple loop in fragment .
int b =0;
for(int i = 0 ; i<n ;i++)
b++;
gl_FragColor = vec4(b,b,b,1.0);
if n is 280 , I got 24
n is 270 14
n is 260 4
n 250 250 is right!
Everyone konw what's wrong with me?
Please tell me some tips or relative site.
Thank you very much!
I found a interesting phenomenon.
I used 2 "for loop" and I can get the right value.
ex:
int b =0;
for(int i =0;i<20;i++)
for(int j =0;j<20;j++)
b++;
I still got the values by glReadPixels ->4e+002.
But the loop became bigger and bigger.
Something wrong!
EX:
250*250
I got 6.25e+004 and it is right!
251*251 is 2.173e+004
252*252 2.173e+004
252*252 2.173e+004
I don't know whats happened.
Please tell me ! Thanks!
Author
Quote:Original post by ARB1130
Hi all:
I try to do computation in shader.
First, I do a FBO object and attatch 4 color + 1 depth texture
my sizes are 725 x 401
Second, I do a simple loop in fragment .
int b =0;
for(int i = 0 ; i<n ;i++)
b++;
gl_FragColor = vec4(b,b,b,1.0);
if n is 280 , I got 24
n is 270 14
n is 260 4
n 250 250 is right!
Everyone konw what's wrong with me?
Please tell me some tips or relative site.
Thank you very much!
I found a strange problem!
In one "for loop",the max value is 256
In two "for loop",the max value >256
Does somebody know the problem?
Thanks to responds! ^_^
This topic is closed to new replies.
Advertisement
Popular Topics
Advertisement
