public void png_set_filter(PNG_FILTER_TYPE method, PNG_FILTER_VALUE filters)
{
if ((mng_features_permitted & PNG_FLAG_MNG.FILTER_64) == PNG_FLAG_MNG.FILTER_64 &&
method == PNG_FILTER_TYPE.INTRAPIXEL_DIFFERENCING)
{
method = PNG_FILTER_TYPE.BASE;
}
if (method != PNG_FILTER_TYPE.BASE)
{
throw new PNG_Exception("Unknown custom filter method");
}
switch (filters)
{
case PNG_FILTER_VALUE.NONE: do_filter = PNG_FILTER.NONE; break;
case PNG_FILTER_VALUE.SUB: do_filter = PNG_FILTER.SUB; break;
case PNG_FILTER_VALUE.UP: do_filter = PNG_FILTER.UP; break;
case PNG_FILTER_VALUE.AVG: do_filter = PNG_FILTER.AVG; break;
case PNG_FILTER_VALUE.PAETH: do_filter = PNG_FILTER.PAETH; break;
default: Debug.WriteLine("Unknown row filter for method 0"); do_filter = PNG_FILTER.NONE; break;
}
png_set_filter2();
}
unsafe void png_read_filter_row(png_row_info row_info, byte[] row, byte[] prev_row, PNG_FILTER_VALUE filter)
{
fixed(byte* row__=row, prev_row__=prev_row)
{
byte* row_=row__+1, prev_row_=prev_row__+1;
switch(filter)
{
case PNG_FILTER_VALUE.NONE: break;
case PNG_FILTER_VALUE.SUB:
{
uint istop=row_info.rowbytes;
uint bpp=(uint)(row_info.pixel_depth+7)>>3;
byte* rp=row_+bpp, lp=row_;
for(uint i=bpp; i<istop; i++)
{
*rp=(byte)(((int)(*rp)+(int)(*lp++))&0xff);
rp++;
}
}
break;
case PNG_FILTER_VALUE.UP:
{
uint istop=row_info.rowbytes;
byte* rp=row_, pp=prev_row_;
for(uint i=0; i<istop; i++)
{
*rp=(byte)(((int)(*rp)+(int)(*pp++))&0xff);
rp++;
}
}
break;
case PNG_FILTER_VALUE.AVG:
{
byte* rp=row_, pp=prev_row_, lp=row_;
uint bpp=(uint)(row_info.pixel_depth+7)>>3;
uint istop=row_info.rowbytes-bpp;
for(uint i=0; i<bpp; i++)
{
*rp=(byte)(((int)(*rp)+((int)(*pp++)/2))&0xff);
rp++;
}
for(uint i=0; i<istop; i++)
{
*rp=(byte)(((int)(*rp)+(int)(*pp+++*lp++)/2)&0xff);
rp++;
}
}
break;
case PNG_FILTER_VALUE.PAETH:
{
byte* rp=row_, pp=prev_row_, lp=row_, cp=prev_row_;
uint bpp=(uint)(row_info.pixel_depth+7)>>3;
uint istop=row_info.rowbytes-bpp;
for(uint i=0; i<bpp; i++)
{
*rp=(byte)(((int)(*rp)+(int)(*pp++))&0xff);
rp++;
}
for(uint i=0; i<istop; i++) // use leftover rp, pp
{
int a=*lp++;
int b=*pp++;
int c=*cp++;
int p=b-c;
int pc=a-c;
//int pa=abs(p);
//int pb=abs(pc);
//pc=abs(p+pc);
int pa=p<0?-p:p;
int pb=pc<0?-pc:pc;
pc=(p+pc)<0?-(p+pc):p+pc;
p=(pa<=pb&&pa<=pc)?a:(pb<=pc)?b:c;
*rp=(byte)(((int)(*rp)+p)&0xff);
rp++;
}
}
break;
default:
Debug.WriteLine("Ignoring bad adaptive filter type");
*row_=0;
break;
}
}
}
public void png_set_filter(PNG_FILTER_TYPE method, PNG_FILTER_VALUE filters)
{
if((mng_features_permitted&PNG_FLAG_MNG.FILTER_64)==PNG_FLAG_MNG.FILTER_64&&
method==PNG_FILTER_TYPE.INTRAPIXEL_DIFFERENCING) method=PNG_FILTER_TYPE.BASE;
if(method!=PNG_FILTER_TYPE.BASE) throw new PNG_Exception("Unknown custom filter method");
switch(filters)
{
case PNG_FILTER_VALUE.NONE: do_filter=PNG_FILTER.NONE; break;
case PNG_FILTER_VALUE.SUB: do_filter=PNG_FILTER.SUB; break;
case PNG_FILTER_VALUE.UP: do_filter=PNG_FILTER.UP; break;
case PNG_FILTER_VALUE.AVG: do_filter=PNG_FILTER.AVG; break;
case PNG_FILTER_VALUE.PAETH: do_filter=PNG_FILTER.PAETH; break;
default: Debug.WriteLine("Unknown row filter for method 0"); do_filter=PNG_FILTER.NONE; break;
}
png_set_filter2();
}
