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Whome · Guest

http://koti.mbnet.fi/akini/delphi/dspack/
file: SampleGrabber.zip

I have edited DSPACK samplegrabber demo to use device capture and
Graphics32 image canvas.

I am not sure about how to use "pBuffer: Pointer" variable most
effective way. See example, now I increment pointer one byte when
traveling through a image size.

Is there a way to cast pBuffer to byte array, without copying a data.
This should create no extra copying 'cause callback method is called
25-50 times per seconds.

What I do here is reading RGB 24-bit pixels and convert to ARGB 32-bit
pixels.

// callback: DirectShow calls this on each video frame
procedure TForm1.SampleGrabberBuffer(sender: TObject; SampleTime: Double;
pBuffer: Pointer; BufferLen: Integer);
var
idx: Integer;
a, r, g, b: Byte;
pb: PByte;
P: PColor32Array;
begin
if CallBack.Checked then begin
Image.Canvas.Lock; // to avoid flickering
G32.Bitmap.Lock;
G32.BeginUpdate;
try
// 1: Use Delphi Image
SampleGrabber.GetBitmap(Image.Picture.Bitmap, pBuffer, BufferLen);

// 2: Use Graphics32 Image
// Logitech webcam RGB24 352x288, 24 bits = 304128 bufferlen
// NOTE: source byte format may change depending on camera
// or "Play File..." file codec being used.
// For now hardcode this format.

prevBufferLen := BufferLen;
P := G32.Bitmap.Bits;

pb := PByte(pBuffer);
Dec(pb, 1); // go back one step, we +1 inc inside for loop
for idx := 0 to G32.Bitmap.Width * G32.Bitmap.Height - 1 do begin
// Logitech gives bytes as BGR (mirrored image)
a := $FF;
Inc(pb, 1); b := byte(pb^);
Inc(pb, 1); g := byte(pb^);
Inc(pb, 1); r := byte(pb^);
p[idx] := (a SHL 24) OR (r SHL 16) OR (g SHL Cool

OR (b);
end;

// Logitech gives a mirrored image, must flip.
// TODO: change for loop to read mirrored bytes.
G32.Bitmap.FlipVert(G32.Bitmap);
finally
Image.Canvas.Unlock;
G32.EndUpdate;
G32.Bitmap.Changed;
G32.Bitmap.Unlock;
end;
end;
end;

Whome · Guest

Ok, I at least managed to read mirrored pixels directly to top-left ARGB
image format and don't have to flipVert or flipHorz at the end.

I think I go with this method, it works anyway.

procedure TForm1.SampleGrabberBuffer(sender: TObject; SampleTime: Double;
pBuffer: Pointer; BufferLen: Integer);
var
row, col: Integer;
idx: Integer;
a, r, g, b: Byte;
pb: PByte;
P: PColor32Array;
begin
if CallBack.Checked then begin
prevBufferLen := BufferLen;
prevSampleTime := SampleTime;

Image.Canvas.Lock; // to avoid flickering
G32.Bitmap.Lock;
G32.BeginUpdate;
try
// 1: Use Delphi Image
SampleGrabber.GetBitmap(Image.Picture.Bitmap, pBuffer, BufferLen);

// 2: Use Graphics32 Image
// Logitech webcam RGB24 352x288, 24 bits = 304128 bufferlen
// NOTE: source byte format may change depending on camera
// or "Play File..." file codec being used.
// For now hardcode this format.

P := G32.Bitmap.Bits;

// read mirrored pixels and copy to top-left ARGB canvas format
pb := PByte(pBuffer);
Inc(pb, BufferLen);
for row := 0 to G32.Bitmap.Height - 1 do begin
for col := 0 to G32.Bitmap.Width - 1 do begin
a := $FF;
Dec(pb, 1); r := byte(pb^);
Dec(pb, 1); b := byte(pb^);
Dec(pb, 1); g := byte(pb^);
p[G32.Bitmap.Width-1-col + (row * G32.Bitmap.Width)] :=
(a SHL 24) OR (r SHL 16) OR (g SHL Cool

OR (b);
end;
end;

// draw transparent rectangle and frame timestamp
G32.Bitmap.FillRectT(0, 10, 200, 40, $8000FF00);
G32.Bitmap.Font.Size := 16;
//G32.Bitmap.Textout(10, 10, 'Time: ' + FloatToStr(sampleTime));
G32.Bitmap.RenderText(10, 10,
'Time: ' + FloatToStr(sampleTime), 4, $FF000000);

finally
Image.Canvas.Unlock;
G32.EndUpdate;
G32.Bitmap.Changed;
G32.Bitmap.Unlock;
end;
end;
end;

Whome wrote: