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Apple II Technical Notes _____________________________________________________________________________ Developer Technical Support Apple IIGS #34: Low-Level QuickDraw II Routines Revised by: Keith Rollin, Steven Glass, Matt Deatherage & Eric Soldan January 1989 Written by: Steven Glass May 1988 This Technical Note describes the low-level routines which QuickDraw II uses to do much of the work in standard calls and mechanisms for calling these routines and accessing their data. Changed since November 1988: Expanded the section on "Dealing with the Cursor" and documented a bug in ShieldCursor. _____________________________________________________________________________ QuickDraw II lets you customize low-level drawing operations by intercepting the "bottleneck procedures." QuickDraw II calls an appropriate "bottleneck proc" every time it receives a call to draw an object, measure text, or deal with pictures. For example, if an application calls PaintOval, QuickDraw II calls StdOval to do the real work, and if an application calls InvertRgn, QuickDraw II calls StdRgn to do the work. Installing your own bottleneck procedures is a little bit tricky. The QuickDraw II SetStdProcs call accepts a pointer to a 56-byte ($38 hex) record and fills that record with the addresses of the standard bottleneck procedures of QuickDraw II. You may modify this record by replacing those addresses with the addresses of your own custom bottleneck procedures minus one. (QuickDraw II pushes the address on the stack and executes an RTL to it, so the address in the record must point to the byte before the routine.) After installing your own procedures, you use SetGrafProcs to tell QuickDraw II about them. The format of this call is as follows (taken from the E16.QUICKDRAW file in APW): ostdText GEQU $00 ; Pointer - QDProcs - ostdLine GEQU $04 ; Pointer - QDProcs - ostdRect GEQU $08 ; Pointer - QDProcs - ostdRRect GEQU $0C ; Pointer - QDProcs - ostdOval GEQU $10 ; Pointer - QDProcs - ostdArc GEQU $14 ; Pointer - QDProcs - ostdPoly GEQU $18 ; Pointer - QDProcs - ostdRgn GEQU $1C ; Pointer - QDProcs - ostdPixels GEQU $20 ; Pointer - QDProcs - ostdComment GEQU $24 ; Pointer - QDProcs - ostdTxMeas GEQU $28 ; Pointer - QDProcs - ostdTxBnds GEQU $2C ; Pointer - QDProcs - ostdGetPic GEQU $30 ; Pointer - QDProcs - ostdPutPic GEQU $34 ; Pointer - QDProcs - The following code fragment shows how you might replace the StdRect procedure with your own for a given window: pha ; open a test window pha PushLong #MWindData ; standard setup for NewWindow _NewWindow _SetPort PushLong #MyProcs ; get a record to modify _SetStdProcs ldy #ostdRect ; get the low word of my rectangle routine lda #myRect-1 ; (minus one) and patch it in to the record sta myProcs,y lda #^myRect ; do the same for the high word sta myProcs+2,y PushLong #MyProcs ; install the procs _SetGrafProcs The interface to bottleneck procedures is different from the interface to other QuickDraw II routines; you do not make calls via the tool dispatcher and you pass most parameters on the direct page and in registers (rather than on the stack). To write your own bottleneck procedures, you have to know where the inputs to each call are kept and how to call the standard procedures from inside your own procedures. The standard bottleneck procedures are accessed through vectors in bank $E0. StdText $E01E04 StdLine $E01E08 StdRect $E01E0C StdRRect $E01E10 StdOval $E01E14 StdArc $E01E18 StdPoly $E01E1C StdRgn $E01E20 StdPixels $E01E24 StdComment $E01E28 StdTxMeas $E01E2C StdTxBnds $E01E30 StdGetPic $E01E34 StdPutPic $E01E38 When you call any of the standard procedures, the first direct page of QuickDraw II is active. If you pass variables on any direct page other than the first (direct page locations greater than $FF), you can use a simple trick to access them. For example, to access TheFillPat ($10E) without changing the direct page register: ldx #$100 ;offset to second DP lda >$OE,X ;gets "DP" location $10E Certain locations on the direct page are always valid: PortRef $24 MaxWidth $20 MasterSCB $08 UserID $0A DrawVerb is usually valid, but not always: DrawVerb $38 Each of the bottleneck procedures uses the direct page differently. QuickDraw II has an interesting bug relating to the standard conic bottleneck procedures. If you replace any of the standard procedures with your own, QuickDraw II does not perform some of the setups it normally would before calling the standard conic procedures (stdRRect, stdOval, stdArc). For example, if you replace StdRect with a custom rectangle routine, but leave the other conic pointers alone (as shown in the code fragment above), QuickDraw II will not do all of the normal setups when calling the standard conic routines. To deal with this bug of QuickDraw II, you must patch out the additional bottleneck procedures and set up those direct pages locations yourself, or the results will not be what you expect. The QuickDraw II direct-page variables you must initialize yourself in this instance are bulleted (o) below. StdText DrawVerb $38 Describes the kind of text to draw. There are three possible values: DrawCharVerb 0 DrawTextVerb 1 DrawCStrVerb 2 TextPtr $DA If the draw verb is DrawTextVerb or DrawCStrVerb, TextPtr points to the text buffer or C string to draw. TextLength $D8 If the draw verb is DrawTextVerb, TextLength contains the number of bytes in the text buffer. CharToDraw $D6 If the draw verb is DrawCharVerb, CharToDraw contains the character to draw. StdLine Y1 $A6 Starting Y value for the line to draw X1 $A8 Starting X value for the line to draw Y2 $AA Ending Y value for the line to draw X2 $AB Ending X value for the line to draw Rect2 $AE Exactly the same thing as Y1, X1, Y2 and X2 in the top, left, bottom, and right of the rectangle StdRect DrawVerb $38 One of the following five drawing verbs: Frame 0 Paint 1 Erase 2 Invert 3 Fill 4 Rect1 $A6 The rectangle to draw in standard form (top, left, bottom, right) TheFillPat $10E The pattern to use for the rectangle if the verb is Fill Note: The QuickDraw II Auxiliary SpecialRect call does not use the rectangle bottleneck procedures. StdRRect DrawVerb $38 One of the following five drawing verbs: Frame 0 Paint 1 Erase 2 Invert 3 Fill 4 Rect1 $A6 The boundary rectangle for the round rectangle OvalRect $295 A copy of the boundary rectangle for the round rectangle OvalHeight $208 The oval height for the rounded part of the round rectangle OvalWidth $20A The oval width for the rounded part of the round rectangle o ArcAngle $D2 Must be 360 o StartAngle $D4 Must be zero TheFillPat $10E The pattern to use for the round rectangle if the verb is Fill StdOval DrawVerb $38 One of the following five drawing verbs: Frame 0 Paint 1 Erase 2 Invert 3 Fill 4 Rect1 $A6 The boundary rectangle for the oval OvalRect $295 A copy of the boundary rectangle for the oval o OvalHeight $208 Must be the height of the oval o OvalWidth $20A Must be the width of the oval o ArcAngle $D2 Must be 360 o StartAngle $D4 Must be zero TheFillPat $10E The pattern to use for the oval if the verb is Fill StdArc DrawVerb $38 One of the following five drawing verbs: Frame 0 Paint 1 Erase 2 Invert 3 Fill 4 Rect1 $A6 The boundary rectangle for the arc o OvalWidth $20A Must be the width of the boundary rectangle for the arc ArcAngle $D2 The number of degrees the arc will sweep StartAngle $D4 The starting position of the arc TheFillPat $10E The pattern to use for the arc if the verb is Fill StdPoly DrawVerb $38 One of the following five drawing verbs: Frame 0 Paint 1 Erase 2 Invert 3 Fill 4 RgnHandleA $50 The handle to the polygon data structure TheFillPat $10E The pattern to use for the polygon if the verb is Fill StdRgn DrawVerb $38 One of the following five drawing verbs: Frame 0 Paint 1 Erase 2 Invert 3 Fill 4 RgnHandleC $70 The handle to the region to draw TheFillPat $10E The pattern to use for the region if the verb is Fill StdPixels SrcLocInfo $CC The LocInfo record for the source pixel map DestLocInfo $0C The LocInfo record for the destination pixel map SrcRect $DC The source rectangle for the operation in local coordinates for the source pixel map (as described in the source LocInfo record) DestRect $1C The destination rectangle for the operation in local coordinates for the destination pixel map (as described in the destination LocInfo record) XferMode $E4 The mode to use for data transfer RgnHandleA $50 The handle to the first region to which drawing is clipped (usually the ClipRgn from the GrafPort) A NIL handle is not allowed. To signify no clipping, pass a handle to the WideOpen region, which is defined as 10 bytes: Length $A (word) -MaxInt -$3FFF (word) -MaxInt -$3FFF (word) +MaxInt +$3FFF (word) +MaxInt +$3FFF (word) RgnHandleB $60 The handle to the second region to which drawing is clipped (usually the VisRgn from the GrafPort) A NIL handle is not allowed. To signify no clipping, pass a handle to the WideOpen region. RgnHandleC $70 The handle to the second region to which drawing is clipped (usually the mask region from the CopyPixels or the PaintPixels call) A NIL handle is not allowed. To signify no clipping, pass a handle to the WideOpen region. StdComment TheKind $A6 The kind of input for the comment TheSize $A8 The number of bytes to put into the picture TheHandle $AA The data to put into the picture StdTxMeas DrawVerb $38 Describes the kind of text to draw. There are three possible values: DrawCharVerb 0 DrawTextVerb 1 DrawCStrVerb 2 TextPtr $DA If the draw verb is DrawTextVerb or DrawCStrVerb, TextPtr points to the text buffer or C string to draw. TextLength $D8 If the draw verb is DrawTextVerb, TextLength contains the number of bytes in the text buffer. CharToDraw $D6 If the draw verb is DrawCharVerb, CharToDraw contains the character to measure. TheWidth $DE The resulting width should be put here. StdTxBnds DrawVerb $38 Describes the kind of text to draw. There are three possible values: DrawCharVerb 0 DrawTextVerb 1 DrawCStrVerb 2 TextPtr $DA If the draw verb is DrawTextVerb or DrawCStrVerb, TextPtr points to the text buffer or C string to draw. TextLength $D8 If the draw verb is DrawTextVerb, TextLength contains the number of bytes in the text buffer. CharToDraw $D6 If the draw verb is DrawCharVerb, CharToDraw contains the character to draw. RectPtr $D2 Indicates the address to put the resulting rectangle. StdGetPic This call takes input on the stack rather than the direct page. This is the one standard bottleneck procedure which you call with the direct page register set to something other than the direct page of QuickDraw II; it is set to a part of the stack. Stack Diagram on Entrance to StdGetPic Previous Contents DataPtr Pointer to destination buffer Count Integer (unsigned) (bytes to read) RTL Address 3 bytes ----------------- Top of Stack Stack Diagram just before exit from StdGetPic Previous Contents RTL Address 3 bytes ----------------- Top of Stack StdPutPic This call takes input on the stack rather than the direct page; however, unlike StdGetPic, the direct page for QuickDraw II is active when you call this routine. Stack Diagram on Entrance to StdPutPic Previous Contents DataPtr Pointer to source buffer Count Integer (unsigned) (bytes to read) RTL Address 3 bytes ----------------- Top of Stack Stack Diagram just before exit from StdPutPic Previous Contents RTL Address 3 bytes ----------------- Top of Stack Dealing with the Cursor The cursor can get in your way when you want to draw directly to the screen. QuickDraw II has two low-level routines which help you avoid this problem: ShieldCursor and UnshieldCursor. ShieldCursor tells QuickDraw II to hide the cursor if it intersects the MinRect and to prevent the cursor from moving until you call UnshieldCursor. There is a bug in ShieldCursor for System Disks 4.0 and earlier. This bug is related to the routine ObscureCursor. When the cursor is obscured, ShieldCursor does not prevent the cursor from moving; therefore, the user is able to move the cursor during a QuickDraw II operation, and this movement may disturb the screen image. Calls to ShieldCursor must be balanced by calls to UnshieldCursor. You may not call ShieldCursor successively without calling UnshieldCursor after each call to ShieldCursor. There is no error checking, so careless use of these routines will result in an unusable system. MinRect is the smallest possible rectangle which encloses all the pixels that may be affected by a drawing call. You keep MinRect on the direct page and usually calculate it by intersecting the rectangle of the object you are drawing with the BoundsRect, PortRect, boundary box of the VisRgn, and the boundary box of the ClipRgn. You must set up MinRect yourself. ShieldCursor also looks at two other fields on the direct page of QuickDraw II. ImageRef is a long word located at $0E. If ImageRef does not point to $E12000, QuickDraw II assumes you are not drawing to the screen, so it does not have to shield the cursor. BoundsRect is a rectangle located at $14, and QuickDraw II uses it to translate MinRect into global coordinates. These values are generally correct, but under the following known circumstance, they are not and ShieldCursor will not function properly: 1. You have just drawn to an off-screen GrafPort with QuickDraw II. 2. You switch to a GrafPort on the screen. 3. You call ShieldCursor. ImageRef and BoundsRect are not updated until QuickDraw II is actually committed to drawing, thus, these values are still for the off-screen GrafPort in this case, even though you switched to a GrafPort on the screen. Therefore, when you call ShieldCursor, you have to make sure that these values are current. (If these values are current, ShieldCursor will work correctly, no matter what the circumstances.) You can find the location of the QuickDraw II direct page with the GetWAP call. For speed reasons, you may not want to make the GetWAP call for each ShieldCursor call. You may wish to get the work area pointer value after starting QuickDraw II and store it for future reference. Calling ShieldCursor: 1. Set direct page for QuickDraw II. 2. Set MinRect, ImageRef, and BoundsRect. 3. Call ShieldCursor. Calling UnshieldCursor: 1. Set direct page for QuickDraw II. 2. Call UnshieldCursor. ShieldCursor $E01E98 MinRect $00 ImageRef $0E BoundsRect $14 UnshieldCursor $E01E9C Further Reference _____________________________________________________________________________ o Apple IIGS Toolbox Reference, Volume 2