Filter SDK/SimpleSample

I have rewritten SimpleSample for AviSynth 2.6. I changed it into an in place filter (so the source is overwritten). It draws a white square in the center of the clip and it supports all colorformats.

Here's simplesample.cpp:

#include <windows.h>
#include "avisynth.h"

class SimpleSample : public GenericVideoFilter {
   int SquareSize;
public:
   SimpleSample(PClip _child,	int _SquareSize, IScriptEnvironment* env);
   ~SimpleSample();
   PVideoFrame __stdcall GetFrame(int n, IScriptEnvironment* env);
};

SimpleSample::SimpleSample(PClip _child, int _SquareSize, IScriptEnvironment* env) :
   GenericVideoFilter(_child), SquareSize(_SquareSize) {
   if (vi.width<SquareSize || vi.height<SquareSize) {
      env->ThrowError("SimpleSample: square doesn't fit into the clip!");
   }
}

SimpleSample::~SimpleSample() {}

PVideoFrame __stdcall SimpleSample::GetFrame(int n, IScriptEnvironment* env) {

   PVideoFrame src = child->GetFrame(n, env);
   env->MakeWritable(&src);

   unsigned char* srcp = src->GetWritePtr();
   int src_pitch = src->GetPitch();
   int src_width = src->GetRowSize();
   int src_height = src->GetHeight();

   int w, h, woffset;

   if (vi.IsRGB24()) {
      srcp = srcp + (src_height/2 - SquareSize/2) * src_pitch;

      woffset = src_width/2 - 3*SquareSize/2;

      for (h=0; h<SquareSize; h++) {
         for (w=0; w<3*SquareSize; w+=3) {
            *(srcp + woffset + w) = 255;
            *(srcp + woffset + w + 1) = 255;
            *(srcp + woffset + w + 2) = 255;
         }															
         srcp += src_pitch;
      }
   }
   if (vi.IsRGB32()) {
      srcp = srcp + (src_height/2 - SquareSize/2) * src_pitch;

      woffset = src_width/2 - 4*SquareSize/2;

      for (h=0; h<SquareSize; h++) {
         for (w=0; w<4*SquareSize; w+=4) {
            *(srcp + woffset + w) = 255;
            *(srcp + woffset + w + 1) = 255;
            *(srcp + woffset + w + 2) = 255;
         }
         srcp += src_pitch;
      }
   }
/*
   if (vi.IsRGB32()) { // variant 1 - processing a pixel at once
      srcp = srcp + (src_height/2 - SquareSize/2) * src_pitch;

      woffset = src_width/8 - SquareSize/2;

      for (h=0; h<SquareSize; h++) {
         for (w=0; w<SquareSize; w++) {
            *((unsigned int *)srcp + woffset + w) = 0x00FFFFFF;
         }	
         srcp += src_pitch;
      }
   }
*/
/*
   if (vi.IsRGB32()) { // variant 2 - processing a pixel at once
      unsigned int* srcp = (unsigned int*)src->GetWritePtr();
	
      srcp = srcp + (src_height/2 - SquareSize/2) * src_pitch/4;

      woffset = src_width/8 - SquareSize/2;

      for (h=0; h<SquareSize; h++) {
         for (w=0; w<SquareSize; w++) {
            srcp[woffset + w] = 0x00FFFFFF;
         }	
         srcp += src_pitch/4;
      }
   }
*/
   if (vi.IsYUY2()) {
      srcp = srcp + (src_height/2 - SquareSize/2) * src_pitch;
	
      woffset = src_width/8 - SquareSize/4;

      for (h=0; h<SquareSize; h++) {
         for (w=0; w<SquareSize/2; w++) {
            *((unsigned int *)srcp + woffset + w) = 0x80EB80EB;
         }
         srcp += src_pitch; 
      }
   }
   if (vi.IsPlanar() && vi.IsYUV()) {

      int planes[] = {PLANAR_Y, PLANAR_U, PLANAR_V};
      int square_value[] = {235, 128, 128};
      int p;
      int width_sub, height_sub;

      for (p=0; p<3; p++) {
         srcp = src->GetWritePtr(planes[p]);		
         src_pitch = src->GetPitch(planes[p]);
         src_width = src->GetRowSize(planes[p]);
         src_height = src->GetHeight(planes[p]);
         width_sub = vi.GetPlaneWidthSubsampling(planes[p]);
         height_sub = vi.GetPlaneHeightSubsampling(planes[p]);
	
         srcp = srcp + (src_height/2 - (SquareSize>>height_sub)/2) * src_pitch;
	
         woffset = src_width/2 - (SquareSize>>width_sub)/2;
	
         for (h=0; h<(SquareSize>>height_sub); h++) {
            for (w=0; w<(SquareSize>>width_sub); w++) {
               srcp[woffset + w] = square_value[p];
            }
            srcp += src_pitch;
         }
      }
   }

   return src;
}

AVSValue __cdecl Create_SimpleSample(AVSValue args, void* user_data, IScriptEnvironment* env) {
   return new SimpleSample(args[0].AsClip(),   
                           args[1].AsInt(100),
                           env); 
}

const AVS_Linkage *AVS_linkage = 0;

extern "C" __declspec(dllexport) const char* __stdcall AvisynthPluginInit3(IScriptEnvironment* env, const AVS_Linkage* const vectors) {
   AVS_linkage = vectors;
   env->AddFunction("SimpleSample", "c[SIZE]i", Create_SimpleSample, 0);
   return "SimpleSample plugin";
}

Compile this file into a DLL named InvertNeg.dll. See compiling instructions. Now create an Avisynth script which looks something like this:

LoadPlugin("d:\path\simplesample.dll")
Colorbars().Trim(0,1)
ConvertTORGB32()
# ConvertTOYV411()
SimpleSample(100)

Line by line breakdown

Here's a line-by-line breakdown of simplesample.cpp. I won't repeat the comments in the previous example InvertNeg.cpp, so read that first if needed. The declaration of the class is as follows

class SimpleSample : public GenericVideoFilter {
   int SquareSize;
public:
   SimpleSample(PClip _child,	int _SquareSize, IScriptEnvironment* env);
   ~SimpleSample();
   PVideoFrame __stdcall GetFrame(int n, IScriptEnvironment* env);
};

With respect to our previous example there are two differences. It contains a private data member 'SquareSize' (members are private by default). Note that this is our parameter variable. These have to be declared here.

The member function ~SimpleSample() is the declaration of the destructor. It fulfills the opposite functionality as the constructor. It is automatically called when the filter is destroyed. It is used to release allocated memory when the filter is destroyed. This is needed when there is memory allocated in the constructor. This is not the case in our filter, so we didn't need to declare it.

SimpleSample::~SimpleSample() {}

This is the actual destructor. You can release allocated memory here using the operator delete.

SimpleSample::SimpleSample(PClip _child, int _SquareSize, IScriptEnvironment* env) :
   GenericVideoFilter(_child), SquareSize(_SquareSize) {
   if (vi.width<SquareSize || vi.height<SquareSize) {
      env->ThrowError("SimpleSample: square doesn't fit into the clip!");
   }
}

This is the constructor. It initializes the value of SquareSize with the parameter that is passed to it (which is called _SquareSize here). It also checks whether the square which will be drawn fits in the frame, otherwise it will return an error.

unsigned char* srcp = src->GetWritePtr(); int src_pitch = src->GetPitch(); // in bytes int src_width = src->GetRowSize(); // in bytes int src_height = src->GetHeight(); // in pixels

The default value of plane is PLANAR_Y (= 0) for the functions GetReadPtr, GetWritePtr, GetPitch, GetRowSize and GetHeight. For planar formats this is the luma plane and for interleaved formats this is the whole frame.

   if (vi.IsRGB24()) {
      srcp = srcp + (src_height/2 - SquareSize/2) * src_pitch;

      woffset = src_width/2 - 3*SquareSize/2;

      for (h=0; h<SquareSize; h++) {
         for (w=0; w<3*SquareSize; w+=3) {
            *(srcp + woffset + w) = 255;     // this is the same as srcp[woffset+w]=255;
            *(srcp + woffset + w + 1) = 255; // this is the same as srcp[woffset+w+1]=255;
            *(srcp + woffset + w + 2) = 255; // this is the same as srcp[woffset+w+2]=255;
         }															
         srcp += src_pitch;
      }
   }

When the clip has color format RGB24 the code above is executed. Each pixel is represented by three bytes, blue, green and red (in that error). RGB is up side down, so srcp[0] will be the bottom-left pixel.

xxx