performance - gdi+ Graphics::DrawImage really slow~~

Question

I am using a GDI+ Graphic to draw a 4000*3000 image to screen, but it is really slow. It takes about 300ms. I wish it just occupy less than 10ms.

Bitmap *bitmap = Bitmap::FromFile("XXXX",...);

//-------------------------------------------- // this part takes about 300ms, terrible!

int width = bitmap->GetWidth();
int height = bitmap->GetHeight();
DrawImage(bitmap,0,0,width,height);

//------------------------------------------

I cannot use CachedBitmap, because I want to edit the bitmap later.

How can I improve it? Or is any thing wrong?

This native GDI function also draws the image into the screen, and it just take 1 ms:

SetStretchBltMode(hDC, COLORONCOLOR);   
StretchDIBits(hDC, rcDest.left, rcDest.top, 
        rcDest.right-rcDest.left, rcDest.bottom-rcDest.top, 
        0, 0, width, height,
        BYTE* dib, dibinfo, DIB_RGB_COLORS, SRCCOPY);

//--------------------------------------------------------------

If I want to use StretchDIBits, I need to pass BITMAPINFO, But how can I get BITMAPINFO from a Gdi+ Bitmap Object? I did the experiment by FreeImage lib, I call StretchDIBits using FreeImageplus object, it draw really fast. But now I need to draw Bitmap, and write some algorithm on Bitmap's bits array, how can I get BITMAPINFO if I have an Bitmap object? It's really annoying -___________-|

Answer 1

If you're using GDI+, the TextureBrush class is what you need for rendering images fast. I've written a couple of 2d games with it, getting around 30 FPS or so.

I've never written .NET code in C++, so here's a C#-ish example:

Bitmap bmp = new Bitmap(...)
TextureBrush myBrush = new TextureBrush(bmp)

private void Paint(object sender, PaintEventArgs e):
{
    //Don't draw the bitmap directly. 
    //Only draw TextureBrush inside the Paint event.
    e.Graphics.FillRectangle(myBrush, ...)
}