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NAME
- CalcIVG
-
Calculate the number of blank lines above a ViewPort (V39)
SYNOPSIS
count = CalcIVG(View, ViewPort)
UWORD CalcIVG(struct View *, struct ViewPort *);
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FUNCTION
To calculate the maximum number of blank lines above a viewport needed to load all the copper instructions, after accounting for the viewport bandwidth and size.
INPUTS
- View
-
pointer to the View
- ViewPort
-
pointer to the ViewPort you are interested in.
RESULT
- count
-
the number of ViewPort resolution scan lines needed to execute all the copper instructions for ViewPort, or 0 if any error.
NOTES
The number of copper instructions comes from the vp->vp_DspIns list. Although there may be other copper instructions in the final list (from UCopIns, SprIns and ClrIns) they are currently ignored for this function. This also means that if the ViewPort has never been made (for example, the ViewPort of an intuition screen was opened behind) then vp->vp_DspIns is NULL.
Although CalcIVG() returns the true number of lines needed by the copper, intuition still maintains an inter-screen gap of 3 non-laced lines (6 interlaced). Therefore, for intuition screens use: MAX(CalcIVG(v, vp), (islaced ? 6 : 3))
Although CalcIVG() returns the true number of lines needed by the copper, intuition still maintains an inter-screen gap of 3 non-laced lines (6 interlaced). Therefore, for intuition screens use: MAX(CalcIVG(v, vp), (islaced ? 6 : 3))