Multiple BitBlt Routines Causing Flicker

[Conroy Vanderbluff]

I have created a subroutine that I can simply call whenever I need to use BitBlt:

Public Function DoBitBlt(theBuffer As PictureBox, THESTAGE As Object, THEBACKGROUND As PictureBox, THECHARACTER As PictureBox, THECHARACTERMASK As PictureBox, theCharacterNewX As Long, theCharacterNewY As Long)
theBuffer.Width = THEBACKGROUND.Width
theBuffer.Height = THEBACKGROUND.Height
THECHARACTERMASK.Width = THECHARACTER.Width
THECHARACTERMASK.Height = THECHARACTER.Height

BitBlt theBuffer.hdc, 0, 0, Val(theBuffer.Width / Screen.TwipsPerPixelX), Val(theBuffer.Height / Screen.TwipsPerPixelY), THEBACKGROUND.hdc, 0, 0, vbSrcCopy

BitBlt theBuffer.hdc, theCharacterNewX, theCharacterNewY, THECHARACTER.Width, THECHARACTER.Height, THECHARACTERMASK.hdc, 0, 0, vbSrcAnd
BitBlt theBuffer.hdc, theCharacterNewX, theCharacterNewY, THECHARACTER.Width, THECHARACTER.Height, THECHARACTER.hdc, 0, 0, vbSrcPaint

BitBlt THESTAGE.hdc, 0, 0, THESTAGE.ScaleWidth, THESTAGE.ScaleHeight, theBuffer.hdc, 0, 0, vbSrcCopy
End Function

In a Timer with an interval of 100, I am calling this subroutine twice (I have two separate pictures I am attempting to BitBlt). If I were to comment out one, the other would work flawlessly. However, when both are called, I get flicker.

One picture is animating. The other picture is non-animating. The problem is if you BitBlt one thing on a PictureBox, you have to do it to everything else that you want to appear. You can't just drop a PictureBox on the scenery picture... it just won't show.

Therefore, my question is: How do I BitBlt two or more pictures (animated and non-animated) without causing flicker?

[Tanner_H]

Hi Conroy. I fear flickering is unavoidable if you render anything less than the full scene directly to the screen. You'll need to render the entire scene to an off-screen buffer, then flip that buffer to the screen after all drawing has finished.

So, two potentially easy fixes would be:

1) Set the .AutoRedraw property of THESTAGE form or picture box to TRUE. After calling DoBitBlt twice (or however many times you need to do it), add this code to the calling function:

THESTAGE.Picture = THESTAGE.Image
THESTAGE.Refresh

That will trigger an AutoRedraw refresh.

2) Instead of rendering directly to THESTAGE, create an off-screen form or picture box called THESTAGEBUFFER. Change DoBitBlt to render to THESTAGEBUFFER, then when all DoBitBlt calls are done, copy THESTAGEBUFFER to THESTAGE.

Are either of those fixes simple to implement in your current rendering chain?