How to detect screen refresh....?

[onrdbandit]

howdy,

I am working on an app that somes physics problems i.e. projectile trajectory etc. and I want to generate simple animations from these calculations.

I have the necessary code to draw the frames to a TCanvas, but I need to detect the screen refreshing, so I can copy the buffered images to the visible TCanvas without "tearing" the images.

Without properly timing the TCanvas->Refresh() function calls, the animation is impossible to see.

thanks in advance
onrdbandit

 

[Supernat03]

What you may be seeing is a Borland Booboo. In their attempt at making the programming interface user friendly, they assume a lot of things, and one of those is in the Microsoft function call InvalidateRect(). There is a parameter called bErase that the TCanvas automatically fills in as true. You want to say false. What it does is erases the background, then redraws the canvas, creating a blinking-like animation.

To solve this, override the Invalidate function and maybe the Update function? I can't remember, I have that info at work, so I'll post it tomorrow. Anyway, you force call InvalidateRect and set that parameter to false. But in your paint function you still double buffer:

void __fastcall Paint(void)
{
static Graphics::TBitmap *BackBuffer = new Graphics::TBitmap();

TRect Rect = Rect(0, 0, Width, Height);
BackBuffer->Width = Width;
BackBuffer->Height = Height;
BackBuffer->Canvas->FillRect(Rect);
BackBuffer->Canvas->LineTo(...);
BackBuffer->Canvas->Ellipse(...);
BackBuffer->Canvas->AllDrawingFunctions(...);

Canvas->Draw(0, 0, BackBuffer);
}

Hope that helps,
Chris

 

[dominochmiel]

Best way to do it is to use Device-Dependent-Bitmap. If you want to know more mail me at dominochmiel@interia.pl

 

[Supernat03]

Nevermind, you don't need to override anything but the Paint method. Just don't call it's ansestor paint method. Be sure that your backbuffer is cleared out too.

Chris