[vte/wip/l2-21235: 3/7] minifont: Implement separated block quadrants

[Christian Persch <chpe src gnome org>]

commit b7ae82fbbe61d313f2fe945957a9d8443e231af2
Author: Christian Persch <chpe src gnome org>
Date:   Thu Apr 7 16:44:09 2022 +0200

    minifont: Implement separated block quadrants

 src/cairo-glue.hh |   1 +
 src/minifont.cc   | 102 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 102 insertions(+), 1 deletion(-)
---
diff --git a/src/cairo-glue.hh b/src/cairo-glue.hh
index 168356ab..5d8be6ee 100644
--- a/src/cairo-glue.hh
+++ b/src/cairo-glue.hh
@@ -23,6 +23,7 @@
 
 namespace vte {
 
+VTE_DECLARE_FREEABLE(cairo_pattern_t, cairo_pattern_destroy);
 VTE_DECLARE_FREEABLE(cairo_rectangle_list_t, cairo_rectangle_list_destroy);
 VTE_DECLARE_FREEABLE(cairo_region_t, cairo_region_destroy);
 VTE_DECLARE_FREEABLE(cairo_surface_t, cairo_surface_destroy);
diff --git a/src/minifont.cc b/src/minifont.cc
index 557e901b..b26a67d1 100644
--- a/src/minifont.cc
+++ b/src/minifont.cc
@@ -20,7 +20,7 @@
 
 #include <cmath>
 
-#include <cairo.h>
+#include "cairo-glue.hh"
 
 #include "drawing-cairo.hh"
 #include "minifont.hh"
@@ -101,6 +101,30 @@ rectangle(cairo_t* cr,
         cairo_fill (cr);
 }
 
+inline void
+quadrant(cairo_t* cr,
+         uint8_t value,
+         int x,
+         int y,
+         int width,
+         int height) noexcept
+{
+        auto const width_half = std::max(width / 2, 1);
+        auto const height_half = std::max(height / 2, 1);
+
+        cairo_set_line_width(cr, 0);
+        if (value & 0b0001u)
+                cairo_rectangle(cr, x, y, width_half, height_half);
+        if (value & 0b0010u)
+                cairo_rectangle(cr, x + width_half, y, width - width_half, height_half);
+        if (value & 0b0100u)
+                cairo_rectangle(cr, x, y + height_half, width_half, height - height_half);
+        if (value & 0b1000u)
+                cairo_rectangle(cr, x + width_half, y + height_half, width - width_half, height - 
height_half);
+
+        cairo_fill(cr);
+}
+
 static void
 polygon(cairo_t* cr,
         double x,
@@ -139,6 +163,74 @@ pattern(cairo_t* cr,
         cairo_mask(cr, pattern);
 }
 
+/* Create separated mosaic patterns.
+ * Transparent pixels will not be drawn; opaque pixels will draw that part of the
+ * mosaic onto the target surface.
+ */
+
+inline vte::Freeable<cairo_pattern_t>
+create_quadrant_separation_pattern(int width,
+                                   int height,
+                                   int line_thickness)
+{
+        auto surface = vte::take_freeable(cairo_image_surface_create(CAIRO_FORMAT_A1, width, height));
+        // or CAIRO_FORMAT_A8, whichever is better/faster?
+
+        auto cr = vte::take_freeable(cairo_create(surface.get()));
+
+        /* It's not quite clear how the separated quadrants should be drawn.
+         *
+         * The L2/21-235 Sources document shows the separation being drawn as
+         * blanking a line on the left and top parts of each 2x2 block.
+         *
+         * Here, we blank a line on the left and *bottom* of each 2x2 block,
+         * for consistency with how we draw the separated sextants / mosaics,
+         * see below.
+         */
+
+        /* First, fill completely with transparent pixels */
+        cairo_set_source_rgba(cr.get(), 0., 0., 0., 0.);
+        cairo_rectangle(cr.get(), 0, 0, width, height);
+        cairo_fill(cr.get());
+
+        /* Now, fill the reduced blocks with opaque pixels */
+
+        auto const pel = line_thickness; /* see the separated sextants below */
+
+        cairo_set_source_rgba(cr.get(), 0., 0., 0., 1.);
+
+        if (width > 2 * pel && height > 2 * pel) {
+
+                auto const width_half = width / 2;
+                auto const height_half = height / 2;
+
+                int const y[3] = { 0, height_half, height };
+                int const x[3] = { 0, width_half, width };
+                // FIXMEchpe: or use 2 * width_half instead of width, so that for width odd,
+                // the extra row of pixels is unlit, and the lit blocks have equal width?
+                // and similar for height?
+
+                for (auto yi = 0; yi < 2; ++yi) {
+                        for (auto xi = 0; xi < 2; xi++) {
+                                cairo_rectangle(cr.get(),
+                                                x[xi] + pel,
+                                                y[yi],
+                                                x[xi+1] - x[xi] - pel,
+                                                y[yi+1] - y[yi] - pel);
+                        }
+                }
+        }
+
+        cairo_fill(cr.get());
+
+        auto pattern = vte::take_freeable(cairo_pattern_create_for_surface(surface.get()));
+
+        cairo_pattern_set_extend(pattern.get(), CAIRO_EXTEND_REPEAT);
+        cairo_pattern_set_filter(pattern.get(), CAIRO_FILTER_NEAREST);
+
+        return pattern;
+}
+
 #include "box_drawing.h"
 
 namespace vte::view {
@@ -1103,6 +1195,14 @@ Minifont::draw_graphic(DrawingContext const& context,
                 break;
         }
 
+        case 0x1cc21 ... 0x1cc2f: { /* separated block quadrant-* */
+                cairo_push_group(cr);
+                quadrant(cr, c - 0x1cc10, x, y, width, height);
+                cairo_pop_group_to_source(cr);
+                cairo_mask(cr, create_quadrant_separation_pattern(width, height, light_line_width).get());
+                break;
+        }
+
         default:
                 cairo_set_source_rgba (cr, 1., 0., 1., 1.);
                 cairo_rectangle(cr, x, y, width, height);