correct handling of interpolated tabs using fractional pixel widths

FossilOrigin-Name: ba691f9e0db0b5b11713f770505e068f0e3a73be

5 files changed, 64 insertions, 44 deletions

diff --git a/ChangeLog b/ChangeLog
index b7bfcd1..238519e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,14 @@
 2003-11-21  Vince Darley <vincentdarley@users.sourceforge.net>
 
+	* generic/tkTextDisp.c: 
+	* generic/tkText.h: 
+	* generic/tkText.c: 
+	* tests/textDisp.test: ensure interpolated tabs are at the same
+	location as the equivalent real tabs, by making use of fractional
+	rather than integer pixel calculations.
+	
+2003-11-21  Vince Darley <vincentdarley@users.sourceforge.net>
+
 	* generic/tkTextDisp.c: prevent wrapped line height calculations 
 	until the widget has actually been given a geometry.
 	
diff --git a/generic/tkText.c b/generic/tkText.c
index 133d88d..c5c8baa 100644
--- a/generic/tkText.c
+++ b/generic/tkText.c
@@ -14,7 +14,7 @@
  * See the file "license.terms" for information on usage and redistribution
  * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
  *
- * RCS: @(#) $Id: tkText.c,v 1.44 2003/11/15 02:33:50 vincentdarley Exp $
+ * RCS: @(#) $Id: tkText.c,v 1.45 2003/11/21 18:51:18 vincentdarley Exp $
  */
 
 #include "default.h"
@@ -3310,6 +3310,7 @@ TkTextGetTabs(interp, tkwin, stringPtr)
     TkTextTabArray *tabArrayPtr;
     TkTextTab *tabPtr;
     Tcl_UniChar ch;
+    double prevStop, lastStop;
 
     /* Map these strings to TkTextTabAlign values */
     
@@ -3342,6 +3343,8 @@ TkTextGetTabs(interp, tkwin, stringPtr)
     tabArrayPtr = (TkTextTabArray *) ckalloc((unsigned)
 	    (sizeof(TkTextTabArray) + (count-1)*sizeof(TkTextTab)));
     tabArrayPtr->numTabs = 0;
+    prevStop = 0.0;
+    lastStop = 0.0;
     for (i = 0, tabPtr = &tabArrayPtr->tabs[0]; i  < objc; i++, tabPtr++) {
 	int index;
 	
@@ -3349,6 +3352,14 @@ TkTextGetTabs(interp, tkwin, stringPtr)
 		!= TCL_OK) {
 	    goto error;
 	}
+	
+	prevStop = lastStop;
+	if (Tk_GetMMFromObj(interp, tkwin, objv[i], &lastStop) != TCL_OK) {
+	    goto error;
+	}
+	lastStop *= WidthOfScreen(Tk_Screen(tkwin));
+	lastStop /= WidthMMOfScreen(Tk_Screen(tkwin));
+	
 	tabArrayPtr->numTabs++;
 
 	/*
@@ -3373,6 +3384,15 @@ TkTextGetTabs(interp, tkwin, stringPtr)
 	}
 	tabPtr->alignment = ((TkTextTabAlign)index);
     }
+    
+    /*
+     * For when we need to interpolate tab stops, store
+     * these two so we know the tab stop size to very
+     * high precision.
+     */
+    tabArrayPtr->lastTab = lastStop;
+    tabArrayPtr->tabIncrement = lastStop - prevStop;
+    
     return tabArrayPtr;
 
     error:
diff --git a/generic/tkText.h b/generic/tkText.h
index ee19ad2..bf79bc7 100644
--- a/generic/tkText.h
+++ b/generic/tkText.h
@@ -10,7 +10,7 @@
  * See the file "license.terms" for information on usage and redistribution
  * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
  *
- * RCS: @(#) $Id: tkText.h,v 1.21 2003/11/15 02:33:50 vincentdarley Exp $
+ * RCS: @(#) $Id: tkText.h,v 1.22 2003/11/21 18:51:18 vincentdarley Exp $
  */
 
 #ifndef _TKTEXT
@@ -474,6 +474,12 @@ typedef struct TkTextTab {
 
 typedef struct TkTextTabArray {
     int numTabs;			/* Number of tab stops. */
+    double lastTab;                     /* The accurate fractional pixel 
+                                         * position of the last tab. */
+    double tabIncrement;                /* The accurate fractional pixel
+                                         * increment between interpolated 
+                                         * tabs we have to create when
+                                         * we exceed numTabs. */
     TkTextTab tabs[1];			/* Array of tabs.  The actual size
 					 * will be numTabs.  THIS FIELD MUST
 					 * BE THE LAST IN THE STRUCTURE. */
diff --git a/generic/tkTextDisp.c b/generic/tkTextDisp.c
index 623570a..b218a79 100644
--- a/generic/tkTextDisp.c
+++ b/generic/tkTextDisp.c
@@ -13,7 +13,7 @@
  * See the file "license.terms" for information on usage and redistribution
  * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
  *
- * RCS: @(#) $Id: tkTextDisp.c,v 1.34 2003/11/21 17:29:13 vincentdarley Exp $
+ * RCS: @(#) $Id: tkTextDisp.c,v 1.35 2003/11/21 18:51:18 vincentdarley Exp $
  */
 
 #include "tkPort.h"
@@ -6596,7 +6596,7 @@ AdjustForTab(textPtr, tabArrayPtr, index, chunkPtr)
     int x, desired, delta, width, decimal, i, gotDigit;
     TkTextDispChunk *chunkPtr2, *decimalChunkPtr;
     CharInfo *ciPtr;
-    int tabX, prev, spaceWidth;
+    int tabX, spaceWidth;
     char *p;
     TkTextTabAlign alignment;
 
@@ -6633,15 +6633,10 @@ AdjustForTab(textPtr, tabArrayPtr, index, chunkPtr)
 	 * from the last two tab positions.
 	 */
 
-	if (tabArrayPtr->numTabs > 1) {
-	    prev = tabArrayPtr->tabs[tabArrayPtr->numTabs-2].location;
-	} else {
-	    prev = 0;
-	}
+	tabX = (int) (tabArrayPtr->lastTab 
+		      + (index + 1 - tabArrayPtr->numTabs) 
+		      * tabArrayPtr->tabIncrement + 0.5);
 	alignment = tabArrayPtr->tabs[tabArrayPtr->numTabs-1].alignment;
-	tabX = tabArrayPtr->tabs[tabArrayPtr->numTabs-1].location
-		+ (index + 1 - tabArrayPtr->numTabs)
-		* (tabArrayPtr->tabs[tabArrayPtr->numTabs-1].location - prev);
     }
 
     if (alignment == LEFT) {
@@ -6780,7 +6775,7 @@ SizeOfTab(textPtr, tabArrayPtr, indexPtr, x, maxX)
     int maxX;				/* X-location of pixel just past the
 					 * right edge of the line. */
 {
-    int tabX, prev, result, index, spaceWidth;
+    int tabX, result, index, spaceWidth;
     TkTextTabAlign alignment;
     
     index = *indexPtr;
@@ -6796,7 +6791,7 @@ SizeOfTab(textPtr, tabArrayPtr, indexPtr, x, maxX)
 
     do {
 	/* 
-	 * We were given the count before this tabs, so increment it
+	 * We were given the count before this tab, so increment it
 	 * first.
 	 */
 	index++;
@@ -6805,18 +6800,12 @@ SizeOfTab(textPtr, tabArrayPtr, indexPtr, x, maxX)
 	    alignment = tabArrayPtr->tabs[index].alignment;
 	} else {
 	    /*
-	     * Ran out of tab stops;  compute a tab position by extrapolating
-	     * from the last two tab positions.
+	     * Ran out of tab stops; compute a tab position by
+	     * extrapolating.
 	     */
-	    
-	    if (tabArrayPtr->numTabs > 1) {
-		prev = tabArrayPtr->tabs[tabArrayPtr->numTabs-2].location;
-	    } else {
-		prev = 0;
-	    }
-	    tabX = tabArrayPtr->tabs[tabArrayPtr->numTabs-1].location
-	      + (index + 1 - tabArrayPtr->numTabs)
-	      * (tabArrayPtr->tabs[tabArrayPtr->numTabs-1].location - prev);
+	    tabX = (int) (tabArrayPtr->lastTab 
+			  + (index + 1 - tabArrayPtr->numTabs) 
+			  * tabArrayPtr->tabIncrement + 0.5);
 	    alignment = tabArrayPtr->tabs[tabArrayPtr->numTabs-1].alignment;
 	}
 	/* 
diff --git a/tests/textDisp.test b/tests/textDisp.test
index 48a4567..31abdd1 100644
--- a/tests/textDisp.test
+++ b/tests/textDisp.test
@@ -6,7 +6,7 @@
 # Copyright (c) 1998-1999 by Scriptics Corporation.
 # All rights reserved.
 #
-# RCS: @(#) $Id: textDisp.test,v 1.21 2003/11/21 17:29:13 vincentdarley Exp $
+# RCS: @(#) $Id: textDisp.test,v 1.22 2003/11/21 18:51:18 vincentdarley Exp $
 
 package require tcltest 2.1
 eval tcltest::configure $argv
@@ -3166,27 +3166,23 @@ test textDisp-27.7 {SizeOfTab procedure, center alignment, wrap -none (potential
     lset res 0 [expr {[lindex $res 0] - $tab}]
     set res
 } [list 0 [expr {$fixedDiff + 18}] 7 $fixedHeight]
-test textDisp-27.7.1 {SizeOfTab procedure, fractional tab interpolation problem} {knownBug textfonts} {
+test textDisp-27.7.1 {SizeOfTab procedure, fractional tab interpolation problem} {
     .t delete 1.0 end
-    set cm [winfo fpixels .t 1c]
-    .t configure -tabs {1c 2c 3c 4c} -wrap none -width 40
-    .t insert 1.0 a\tb\tc\td\te\n012345678934567890a\tbb\tcc\tdd
-    set width [expr {$fixedWidth * 19}]
-    set tab $cm
-    while {$tab < $width} {
-	set tab [expr {$tab + $cm}]
+    set interpolatetab {1c 2c}
+    set precisetab {}
+    for {set i 1} {$i < 20} {incr i} {
+	lappend precisetab "${i}c"
     }
-    # Now we've calculated to the end of the tab after 'a', add one
-    # more for 'bb\t' and we're there, with 4 for the border
-    set tab [expr {4 + int($tab + $cm)}]
+    .t configure -tabs $interpolatetab -wrap none -width 150
+    .t insert 1.0 [string repeat "a\t" 20]
     update
-    set res [.t bbox 2.23]
-    # Now, on some platforms Tk interpolated from 3c-4c->5c but that
-    # interpolation doesn't use fractional pixels and so this result
-    # might be off by one.
-    lset res 0 [expr {[lindex $res 0] - $tab}]
-    set res
-} [list 0 [expr {$fixedDiff + 18}] 7 $fixedHeight]
+    set res [.t bbox 1.20]
+    # Now, Tk's interpolated tabs should be the same as
+    # non-interpolated.
+    .t configure -tabs $precisetab
+    update
+    expr {[lindex $res 0] - [lindex [.t bbox 1.20] 0]}
+} {0}
 
 .t configure -wrap char -tabs {} -width 20
 update