CSS/lvrend: adds "-cr-hint: cjk-tailored"

To get paragraphs ("final" blocks) width and text-indent
ajusted to an integer multiple of their font size (so
text justification of lines made of only squared CJK
glyphs get less chance to need to spread the glyphs).

crengine/include/cssdef.h

@@ -394,6 +394,10 @@ enum css_generic_value_t {
 // Glyphs should not overflow line edges, and across text nodes or over images
 // (it can also be used to disable hanging punctuation on the targeted nodes).
 #define CSS_CR_HINT_FIT_GLYPHS              0x00000004 // -cr-hint: fit-glyphs (inheritable)
+// Paragraphs ("final" blocks') width and text-indent is to be ajusted to an
+// integer multiple of their font size (so text justification of lines made of
+// only squared CJK glyphs get less chance to need to spread the glyphs).
+#define CSS_CR_HINT_CJK_TAILORED            0x00000008 // -cr-hint: cjk-tailored (inheritable)
 
 // A node with these should be considered as TOC item of level N when building alternate TOC
 #define CSS_CR_HINT_TOC_LEVEL1              0x00000100 // -cr-hint: toc-level1
@@ -432,7 +436,7 @@ enum css_generic_value_t {
                                                        //                           everything else indicates it is)
 
 // A few of them are inheritable, most are not.
-#define CSS_CR_HINT_INHERITABLE_MASK        0x00000006
+#define CSS_CR_HINT_INHERITABLE_MASK        0x0000000E
 
 // Macro for easier checking
 #define STYLE_HAS_CR_HINT(s, h)     ( (bool)(s->cr_hint.value & CSS_CR_HINT_##h) )

crengine/src/lvrend.cpp

@@ -3316,6 +3316,54 @@ void renderFinalBlock( ldomNode * enode, LFormattedText * txform, RenderRectAcce
             // todo: pass indent via txform->setTextIndent() (like we do for the strut
             // below, and get rid of it in AddSourceLine())
             indent = lengthToPx(enode, style->text_indent, width);
+            if ( STYLE_HAS_CR_HINT(style, CJK_TAILORED) && indent != 0 ) {
+                // We want the text-indent to be an integer multiple of the font size,
+                // so that we may get CJK squared glyphs vertically aligned ensuring
+                // the CJK grid.
+                // (Should letter-spacing be taken into account if set on the paragraph?)
+                int unit = em;
+                int cjk_width_scale_percent = enode->getDocument()->getCJKWidthScalePercent();
+                if ( cjk_width_scale_percent != 100 ) {
+                    unit = unit * cjk_width_scale_percent / 100;
+                    // Recompute indent base on this scaled em
+                    indent = lengthToPx(enode, style->text_indent, width, unit);
+                }
+                bool is_negative = false;
+                if ( indent < 0 ) {
+                    is_negative = true;
+                    indent = -indent; // (to work with positive values)
+                }
+                int tailored_indent = (indent / unit) * unit; // floor'ed
+                if ( tailored_indent != indent ) { // it was a fractional value
+                    if ( tailored_indent == 0 ) { // it was non-zero but less than 1em
+                        tailored_indent = unit; // make it at least 1em
+                    }
+                    else {
+                        // Our epub.css text-indent is 1.2em, and is what will be used when
+                        // a publisher does not specify anything (and if he does, he will
+                        // surely use his preferred integer value).
+                        // clreq mentions: "For Chinese publications, a first-line indent usually uses
+                        // two character width spaces. Publications like magazines, with multi-column
+                        // content and less text in each column, might apply single character width
+                        // first-line indents as well.
+                        // jlreq is vague (and mixed as it talks more about vertical writting mode),
+                        // but mentions: "The amount of spacing used for the indentation is, in
+                        // principle, one em spacing"
+                        // klreq don't mention anything, but its examples use mostly 1 char width.
+                        // So it feels that Chinese would like 2em while Japanese and Korean would
+                        // prefer 1em - but let's not bother for now: go with ceiling to get 2em.
+                        // But stay on the smaller side if the paragraph width is itself small (it
+                        // might be a table cell or a float)
+                        if ( width >= 8*unit ) {
+                            tailored_indent += unit;
+                        }
+                    }
+                    indent = tailored_indent;
+                }
+                if ( is_negative ) {
+                    indent = -indent; // (restore it)
+                }
+            }
             // lvstsheet sets the lowest bit to 1 when text-indent has the "hanging" keyword:
             if ( style->text_indent.value & 0x00000001 ) {
                 // lvtextfm handles negative indent as "indent by the negated (so, then
@@ -8230,9 +8278,28 @@ void renderBlockElementEnhanced( FlowState * flow, ldomNode * enode, int x, int
                 if ( flow->hasActiveFloats() )
                     flow->pushVerticalMargin();
 
-                // Store these in RenderRectAccessor fields, to avoid having to
-                // compute them again when in XPointer, elementFromPoint...
                 int inner_width = width - padding_left - padding_right;
+
+                if ( STYLE_HAS_CR_HINT(style, CJK_TAILORED) ) {
+                    // We want inner_width to be an integer multiple of the font size,
+                    // so that text justification of CJK only lines doesn't need to
+                    // add space between glyphs.
+                    int unit = em;
+                    int cjk_width_scale_percent = enode->getDocument()->getCJKWidthScalePercent();
+                    if ( cjk_width_scale_percent != 100 ) {
+                        unit = unit * cjk_width_scale_percent / 100;
+                    }
+                    int tailored_inner_width = (inner_width / unit) * unit;
+                    // Put half the delta in each padding.
+                    int d_width = inner_width - tailored_inner_width;
+                    padding_left += d_width / 2;
+                    padding_right += d_width - d_width / 2;
+                    inner_width = tailored_inner_width;
+                    // Note: changes in width inside a paragraphs (because of floats)
+                    // are currently not tailored in lvtextfm.cpp (it feels quite
+                    // complicated to do right).
+                }
+
                 if (inner_width <= 0) {
                     // inner_width is the width given to LFormattedText->Format()
                     // to lay out inlines and text along this width.
@@ -8269,6 +8336,8 @@ void renderBlockElementEnhanced( FlowState * flow, ldomNode * enode, int x, int
                     // but it is costly and may result in adding many many pages
                     // with a narrow column of words.
                 }
+                // Store these in RenderRectAccessor fields, to avoid having to
+                // compute them again when in XPointer, elementFromPoint...
                 fmt.setInnerX( padding_left );
                 fmt.setInnerY( padding_top );
                 fmt.setInnerWidth( inner_width );

crengine/src/lvstsheet.cpp

@@ -3089,6 +3089,7 @@ bool LVCssDeclaration::parse( const char * &decl, bool higher_importance, lxmlDo
                         else if ( substr_icompare("non-linear", decl) )             hints |= CSS_CR_HINT_NON_LINEAR;
                         else if ( substr_icompare("non-linear-combining", decl) )   hints |= CSS_CR_HINT_NON_LINEAR_COMBINING;
                         else if ( substr_icompare("strut-confined", decl) )         hints |= CSS_CR_HINT_STRUT_CONFINED;
+                        else if ( substr_icompare("cjk-tailored", decl) )           hints |= CSS_CR_HINT_CJK_TAILORED;
                         else if ( substr_icompare("fit-glyphs", decl) )             hints |= CSS_CR_HINT_FIT_GLYPHS;
                         else if ( substr_icompare("text-selection-skip", decl) )    hints |= CSS_CR_HINT_TEXT_SELECTION_SKIP;
                         else if ( substr_icompare("text-selection-inline", decl) )  hints |= CSS_CR_HINT_TEXT_SELECTION_INLINE;