关于libpng解码速度的优化

由于png没有硬件解码，特别是大尺寸的png图片的解码时间比较长，使用浮点优化以后，速度有明显改善。

方法是在libpng和zlib的makefile中的CFLAG 加上-DPNG_FLOATING_POINT_SUPPORTED -mfpu=vfpv3-d16 -mfloat-abi=softfp -O3 -funroll-loops -fomit-frame-pointer -ffast-math

 

另外再修改directfb的idirectfbp_w_picpathprovider_png.c的IDirectFBImageProvider_PNG_RenderTo()函数中添加时间打印

    struct timeval tv;
    float render_start, render_end, decoder_end, decoder_time, render_time;
   

   gettimeofday(&tv, NULL);
   render_start = (float) (tv.tv_sec) + (float) (tv.tv_usec) / 1000000; 

......

gettimeofday(&tv, NULL);
     decoder_end = (float) (tv.tv_sec) + (float) (tv.tv_usec) / 1000000;
     
     /* actual rendering */

......

 gettimeofday(&tv, NULL);
     render_end = (float) (tv.tv_sec) + (float) (tv.tv_usec) / 1000000;
     decoder_time = decoder_end - render_start;
     render_time = render_end - decoder_end;
     printf("\n Time Taken in Png Decoding: %f seconds\n",decoder_time);
     printf("\n Time Taken in Png Render: %f seconds\n",render_time);
 结果如下：

1.未优化前，运行dfb_neo

 

Time Taken in Jpeg Decoding: 0.054200 seconds
(*) Direct/Interface: Using 'PNG' implementation of 'IDirectFBImageProvider'.

 Time Taken in Png Decoding: 0.004192 seconds

 Time Taken in Png Render: 0.000473 seconds

 Time Taken in Png Decoding: 0.003410 seconds

 Time Taken in Png Render: 0.000420 seconds

 Time Taken in Png Decoding: 0.003462 seconds

 Time Taken in Png Render: 0.000420 seconds

 Time Taken in Png Decoding: 0.003510 seconds

 Time Taken in Png Render: 0.000423 seconds

 Time Taken in Png Decoding: 0.003885 seconds

 Time Taken in Png Render: 0.000431 seconds

 Time Taken in Png Decoding: 0.003639 seconds

 Time Taken in Png Render: 0.000422 seconds

 Time Taken in Png Decoding: 0.004333 seconds

 Time Taken in Png Render: 0.000418 seconds

 Time Taken in Png Decoding: 0.003736 seconds

 Time Taken in Png Render: 0.000427 seconds

 

2.libpng优化以后：

 

 Time Taken in Jpeg Decoding: 0.055157 seconds
(*) Direct/Interface: Using 'PNG' implementation of 'IDirectFBImageProvider'.

 Time Taken in Png Decoding: 0.003592 seconds

 Time Taken in Png Render: 0.000477 seconds

 Time Taken in Png Decoding: 0.002720 seconds

 Time Taken in Png Render: 0.000420 seconds

 Time Taken in Png Decoding: 0.002691 seconds

 Time Taken in Png Render: 0.000441 seconds

 Time Taken in Png Decoding: 0.002802 seconds

 Time Taken in Png Render: 0.000456 seconds

 Time Taken in Png Decoding: 0.003124 seconds

 Time Taken in Png Render: 0.000422 seconds

 Time Taken in Png Decoding: 0.002975 seconds

 Time Taken in Png Render: 0.000422 seconds

 Time Taken in Png Decoding: 0.003540 seconds

 Time Taken in Png Render: 0.000422 seconds

 Time Taken in Png Decoding: 0.003166 seconds

 Time Taken in Png Render: 0.000423 seconds

 

3.libpng和zlib都优化以后：

 

Time Taken in Jpeg Decoding: 0.054309 seconds
(*) Direct/Interface: Using 'PNG' implementation of 'IDirectFBImageProvider'.

 Time Taken in Png Decoding: 0.001759 seconds

 Time Taken in Png Render: 0.000479 seconds

 Time Taken in Png Decoding: 0.001179 seconds

 Time Taken in Png Render: 0.000418 seconds

 Time Taken in Png Decoding: 0.001266 seconds

 Time Taken in Png Render: 0.000412 seconds

 Time Taken in Png Decoding: 0.001179 seconds

 Time Taken in Png Render: 0.000420 seconds

 Time Taken in Png Decoding: 0.001324 seconds

 Time Taken in Png Render: 0.000420 seconds

 Time Taken in Png Decoding: 0.001316 seconds

 Time Taken in Png Render: 0.000422 seconds

 Time Taken in Png Decoding: 0.001591 seconds

 Time Taken in Png Render: 0.000420 seconds

 Time Taken in Png Decoding: 0.001381 seconds

 Time Taken in Png Render: 0.000431 seconds