DeskTop: Fix highlighting when dragging over icons. Fixes #163

The DeskTop library routines for handling icons switched GrafPorts
in a fragile way, which previous changes had broken. Updates to
the volume icon clipping code left the GrafPort used for icon
drawing clipped, and it was not restored correctly before subsequent
file icons were drawn.

Ensure the correct grafports are used everywhere, and reset them
when necessary. Further simplification is possible.

desktop/desktop_aux.s

@@ -672,7 +672,6 @@ found:  asl     a
 
         ;; Unhighlight
 :       jsr     calc_icon_poly
-        MGTK_CALL MGTK::SetPenMode, pencopy
         jsr     draw_icon
 
         ;; Move it to the end of the icon list
@@ -1115,7 +1114,8 @@ is_drag:
         and     #icon_entry_winid_mask
         sta     L9832
 
-        ;; Prepare grafport
+        ;; Prepare grafports
+        MGTK_CALL MGTK::InitPort, icon_grafport
         MGTK_CALL MGTK::InitPort, drag_outline_grafport
         MGTK_CALL MGTK::SetPort, drag_outline_grafport
         MGTK_CALL MGTK::SetPattern, checkerboard_pattern
@@ -1279,6 +1279,7 @@ L9A31:  COPY_BYTES 4, findwindow_params2, L9C92
         cmp     highlight_icon_id
         beq     L9A84
         jsr     xdraw_outline
+        MGTK_CALL MGTK::SetPort, icon_grafport
         DESKTOP_DIRECT_CALL DT_UNHIGHLIGHT_ICON, highlight_icon_id
         jsr     xdraw_outline
         lda     #0
@@ -1359,11 +1360,12 @@ L9B9C:  jsr     xdraw_outline
 
 L9BA5:  jsr     xdraw_outline
         lda     highlight_icon_id
-        beq     L9BB9
+        beq     :+
+        MGTK_CALL MGTK::SetPort, icon_grafport
         DESKTOP_DIRECT_CALL DT_UNHIGHLIGHT_ICON, highlight_icon_id
         jmp     L9C63
 
-L9BB9:  MGTK_CALL MGTK::FindWindow, findwindow_params2
+:       MGTK_CALL MGTK::FindWindow, findwindow_params2
         lda     findwindow_params2::window_id
         cmp     L9832
         beq     L9BE1
@@ -1380,8 +1382,6 @@ L9BD4:  ora     #$80
 L9BDC:  lda     L9832
         beq     L9BD1
 L9BE1:  jsr     push_pointers
-        MGTK_CALL MGTK::InitPort, grafport
-        MGTK_CALL MGTK::SetPort, grafport
         ldx     highlight_count
 L9BF3:  dex
         bmi     L9C18
@@ -1392,7 +1392,6 @@ L9BF3:  dex
         tax
         copy16  icon_ptrs,x, $06
         jsr     calc_icon_poly
-        MGTK_CALL MGTK::SetPenMode, pencopy
         jsr     draw_icon
         pla
         tax
@@ -1561,7 +1560,7 @@ L9E1A:  jsr     push_pointers
         bne     L9E2B
         sta     findwindow_params2::window_id
 L9E2B:  DESKTOP_DIRECT_CALL DT_FIND_ICON, findwindow_params2
-        lda     findwindow_params2::which_area
+        lda     findwindow_params2::which_area ; Icon ID
         bne     L9E39
         jmp     L9E97
 
@@ -1572,8 +1571,8 @@ L9E3D:  cmp     highlight_list,x
         dex
         bpl     L9E3D
         sta     L9EB3
-        cmp     #1
+        cmp     #1              ; Trash?
-        beq     L9E6A
+        beq     :+
         asl     a
         tax
         copy16  icon_ptrs,x, $06
@@ -1585,8 +1584,9 @@ L9E3D:  cmp     highlight_list,x
         and     #icon_entry_type_mask
         bne     L9E97
         lda     L9EB3
-L9E6A:  sta     highlight_icon_id
+:       sta     highlight_icon_id
         jsr     xdraw_outline
+        MGTK_CALL MGTK::SetPort, icon_grafport
         DESKTOP_DIRECT_CALL DT_HIGHLIGHT_ICON, highlight_icon_id
         jsr     xdraw_outline
 L9E97:  jsr     pop_pointers
@@ -1603,7 +1603,6 @@ L9EB4:  asl     a
 .proc xdraw_outline
         MGTK_CALL MGTK::SetPort, drag_outline_grafport
         MGTK_CALL MGTK::FramePoly, drag_outline_buffer
-        MGTK_CALL MGTK::SetPort, grafport
         rts
 .endproc
 
@@ -1808,20 +1807,20 @@ highlighted:  copy    #$80, icon_flags ; is highlighted
         COPY_STRUCT MGTK::Point, moveto_params2, L9F94
 
         bit     icon_flags      ; volume icon (on desktop) ?
-        bvc     paint_icon      ; nope
+        bvc     do_paint        ; nope
 
         ;; Redraw desktop background
         MGTK_CALL MGTK::InitPort, grafport
         jsr     set_port_for_vol_icon
 :       jsr     calc_window_intersections
-        jsr     paint_icon
+        jsr     do_paint
         lda     more_drawing_needed_flag
         bne     :-
-        MGTK_CALL MGTK::SetPortBits, grafport
+        MGTK_CALL MGTK::SetPortBits, grafport ; default maprect
         rts
 .endproc
 
-.proc paint_icon
+.proc do_paint
         MGTK_CALL MGTK::HideCursor
 
         ;; --------------------------------------------------
@@ -2224,8 +2223,8 @@ stash:  .word   0
 ;;; ============================================================
 
 draw_icon:
-        MGTK_CALL MGTK::InitPort, grafport
+        MGTK_CALL MGTK::InitPort, icon_grafport
-        MGTK_CALL MGTK::SetPort, grafport
+        MGTK_CALL MGTK::SetPort, icon_grafport
         jmp     LA3B9
 
 LA3AC:  .byte   0
@@ -2277,7 +2276,7 @@ volume:
         jsr     erase_desktop_icon
         lda     more_drawing_needed_flag
         bne     :-
-        MGTK_CALL MGTK::SetPortBits, grafport
+        MGTK_CALL MGTK::SetPortBits, grafport ; default maprect
         jmp     LA446
 .endproc
 
@@ -2313,7 +2312,7 @@ LA446:  jsr     push_pointers
         bne     LA466
         bit     LA3B7           ; no, almost done
         bpl     :+
-        MGTK_CALL MGTK::InitPort, grafport
+        MGTK_CALL MGTK::InitPort, icon_grafport
         MGTK_CALL MGTK::SetPort, icon_grafport
 :       jsr     pop_pointers
         rts
@@ -2896,8 +2895,11 @@ vert:   cmp16   win_t, cr_t
 ;;; ============================================================
 
 .proc shift_port_down
-        add16   icon_grafport::viewloc::ycoord, #15, icon_grafport::viewloc::ycoord
+        ;; For window's used/free space bar
-        add16   icon_grafport::cliprect::y1, #15, icon_grafport::cliprect::y1
+        offset = 15
+
+        add16   icon_grafport::viewloc::ycoord, #offset, icon_grafport::viewloc::ycoord
+        add16   icon_grafport::cliprect::y1, #offset, icon_grafport::cliprect::y1
         MGTK_CALL MGTK::SetPort, icon_grafport
         rts
 .endproc