Cleanup and comment HarfBuzz code.

1 files changed, 92 insertions, 45 deletions

diff --git a/src/entry_backend/harfbuzz.c b/src/entry_backend/harfbuzz.c
index 03e9ed0..161cefa 100644
--- a/src/entry_backend/harfbuzz.c
+++ b/src/entry_backend/harfbuzz.c
@@ -6,17 +6,38 @@
 #include <pango/pangocairo.h>
 #include <pango/pango.h>
 #include <wchar.h>
+#include "harfbuzz.h"
 #include "../entry.h"
 #include "../log.h"
 #include "../nelem.h"
 #include "../xmalloc.h"
 
 /*
+ * FreeType is normally compiled without error strings, so we have to do this
+ * funky macro trick to get them. See <freetype/fterrors.h> for more details.
+ */
+#undef FTERRORS_H_
+#define FT_ERRORDEF( e, v, s )  { e, s },
+#define FT_ERROR_START_LIST     {
+#define FT_ERROR_END_LIST       { 0, NULL } };
+
+const struct {
+	int err_code;
+	const char *err_msg;
+} ft_errors[] =
+
+#include <freetype/fterrors.h>
+
+/*
  * Cairo / FreeType use 72 Pts per inch, but Pango uses 96 DPI, so we have to
  * rescale for consistency.
  */
 #define PT_TO_DPI (96.0 / 72.0)
 
+/*
+ * hb_buffer_clear_contents also clears some basic script information, so group
+ * them here for convenience.
+ */
 static void setup_hb_buffer(hb_buffer_t *buffer)
 {
 	hb_buffer_set_direction(buffer, HB_DIRECTION_LTR);
@@ -25,39 +46,36 @@ static void setup_hb_buffer(hb_buffer_t *buffer)
 }
 
 
-static hb_buffer_t *create_hb_buffer(void)
-{
-	hb_buffer_t *buffer = hb_buffer_create();
-	hb_buffer_set_unicode_funcs(buffer, hb_glib_get_unicode_funcs());
-	setup_hb_buffer(buffer);
-
-	return buffer;
-}
-
+/*
+ * Render a hb_buffer with Cairo, and return the width of the rendered area in
+ * Cairo units.
+ */
 static uint32_t render_hb_buffer(cairo_t *cr, hb_buffer_t *buffer, uint32_t scale)
 {
 	cairo_save(cr);
 
+	/*
+	 * Cairo uses y-down coordinates, but HarfBuzz uses y-up, so we
+	 * shift the text down by its ascent height to compensate.
+	 */
 	cairo_font_extents_t font_extents;
 	cairo_font_extents(cr, &font_extents);
-	cairo_matrix_t font_matrix;
-	cairo_get_font_matrix(cr, &font_matrix);
-	double baseline = (font_matrix.xx - font_extents.height) / 2 + font_extents.ascent;
-	cairo_translate(cr, 0, baseline);
+	cairo_translate(cr, 0, font_extents.ascent);
 
 	unsigned int glyph_count;
 	hb_glyph_info_t *glyph_info = hb_buffer_get_glyph_infos(buffer, &glyph_count);
 	hb_glyph_position_t *glyph_pos = hb_buffer_get_glyph_positions(buffer, &glyph_count);
 	cairo_glyph_t *cairo_glyphs = xmalloc(sizeof(cairo_glyph_t) * glyph_count);
 
-	double width = 0;
-	for (unsigned int i=0; i < glyph_count; ++i) {
-		width += glyph_pos[i].x_advance / 64.0 / scale;
-	}
-
 	double x = 0;
 	double y = 0;
-	for (unsigned int i=0; i < glyph_count; ++i) {
+	for (unsigned int i=0; i < glyph_count; i++) {
+		/*
+		 * The coordinates returned by HarfBuzz are in 26.6 fixed-point
+		 * format, so we divide by 64.0 (2^6) to get floats.
+		 * We also divide by the display's scale factor, to counter
+		 * Cairo's scaling of coordinates and sizes.
+		 */
 		cairo_glyphs[i].index = glyph_info[i].codepoint;
 		cairo_glyphs[i].x = x + glyph_pos[i].x_offset / 64.0 / scale;
 		cairo_glyphs[i].y = y - glyph_pos[i].y_offset / 64.0 / scale;
@@ -71,28 +89,54 @@ static uint32_t render_hb_buffer(cairo_t *cr, hb_buffer_t *buffer, uint32_t scal
 
 	cairo_restore(cr);
 
+	double width = 0;
+	for (unsigned int i=0; i < glyph_count; i++) {
+		width += glyph_pos[i].x_advance / 64.0 / scale;
+	}
 	return ceil(width);
 }
 
-void entry_backend_init(struct entry *entry, uint32_t *width, uint32_t *height, uint32_t scale)
+void entry_backend_init(
+		struct entry *entry,
+		uint32_t *width,
+		uint32_t *height,
+		uint32_t scale)
 {
 	cairo_t *cr = entry->cairo[0].cr;
 
 	/* Setup FreeType. */
 	log_debug("Creating FreeType library.\n");
-	FT_Init_FreeType(&entry->backend.ft_library);
+	int err;
+	err = FT_Init_FreeType(&entry->backend.ft_library);
+	if (err) {
+		log_error("Error initialising FreeType: %s\n",
+				ft_errors[err].err_msg);
+		exit(EXIT_FAILURE);
+	}
 
 	log_debug("Loading FreeType font.\n");
-	FT_New_Face(entry->backend.ft_library, "font.ttf", 0, &entry->backend.ft_face);
-	FT_Set_Char_Size(
+	err = FT_New_Face(
+			entry->backend.ft_library, "font.ttf", 0,
+			&entry->backend.ft_face);
+	if (err) {
+		log_error("Error loading font: %s\n", ft_errors[err].err_msg);
+		exit(EXIT_FAILURE);
+	}
+	err = FT_Set_Char_Size(
 			entry->backend.ft_face,
-			entry->font_size * 64 * scale * PT_TO_DPI,
-			entry->font_size * 64 * scale * PT_TO_DPI,
-			0,
-			0);
+			entry->font_size * 64 * scale,
+			entry->font_size * 64 * scale,
+			96,
+			96);
+	if (err) {
+		log_error("Error setting font size: %s\n",
+				ft_errors[err].err_msg);
+		exit(EXIT_FAILURE);
+	}
 
 	log_debug("Creating Cairo font.\n");
-	entry->backend.cairo_face = cairo_ft_font_face_create_for_ft_face(entry->backend.ft_face, 0);
+	entry->backend.cairo_face =
+		cairo_ft_font_face_create_for_ft_face(entry->backend.ft_face, 0);
 
 	struct color color = entry->foreground_color;
 	cairo_set_source_rgba(cr, color.r, color.g, color.b, color.a);
@@ -104,18 +148,22 @@ void entry_backend_init(struct entry *entry, uint32_t *width, uint32_t *height,
 	cairo_set_font_size(entry->cairo[1].cr, entry->font_size * PT_TO_DPI);
 
 	log_debug("Creating Harfbuzz font.\n");
-	entry->backend.hb_font = hb_ft_font_create_referenced(entry->backend.ft_face);
+	entry->backend.hb_font =
+		hb_ft_font_create_referenced(entry->backend.ft_face);
 
 	log_debug("Creating Harfbuzz buffer.\n");
-	entry->backend.hb_buffer = create_hb_buffer();
+	hb_buffer_t *buffer = hb_buffer_create();
+	entry->backend.hb_buffer = buffer;
+	hb_buffer_set_unicode_funcs(buffer, hb_glib_get_unicode_funcs());
+	setup_hb_buffer(buffer);
 
 	/* Draw the prompt now, as this only needs to be done once */
 	log_debug("Drawing prompt.\n");
 	hb_buffer_add_utf8(entry->backend.hb_buffer, "run: ", -1, 0, -1);
 	hb_shape(entry->backend.hb_font, entry->backend.hb_buffer, NULL, 0);
+	uint32_t prompt_width = render_hb_buffer(cr, buffer, scale);
 
-	/* Move and clip so we don't draw over the prompt */
-	uint32_t prompt_width = render_hb_buffer(cr, entry->backend.hb_buffer, scale);
+	/* Move and clip so we don't draw over the prompt later */
 	cairo_translate(cr, prompt_width, 0);
 	*width -= prompt_width;
 	cairo_rectangle(cr, 0, 0, *width, *height);
@@ -133,27 +181,26 @@ void entry_backend_destroy(struct entry *entry)
 void entry_backend_update(struct entry *entry)
 {
 	cairo_t *cr = entry->cairo[entry->index].cr;
+	hb_buffer_t *buffer = entry->backend.hb_buffer;
 
-	hb_buffer_clear_contents(entry->backend.hb_buffer);
-	setup_hb_buffer(entry->backend.hb_buffer);
-	hb_buffer_add_utf8(entry->backend.hb_buffer, entry->input_mb, -1, 0, -1);
-	hb_shape(entry->backend.hb_font, entry->backend.hb_buffer, NULL, 0);
-	render_hb_buffer(cr, entry->backend.hb_buffer, entry->image.scale);
+	/* Render the entry text */
+	hb_buffer_clear_contents(buffer);
+	setup_hb_buffer(buffer);
+	hb_buffer_add_utf8(buffer, entry->input_mb, -1, 0, -1);
+	hb_shape(entry->backend.hb_font, buffer, NULL, 0);
+	render_hb_buffer(cr, buffer, entry->image.scale);
 
 	cairo_font_extents_t font_extents;
 	cairo_font_extents(cr, &font_extents);
 
-	for (size_t i = 0; i < 5; i++) {
+	/* Render our results entry text */
+	for (size_t i = 0; i < 5 && i < entry->results.count; i++) {
 		cairo_translate(cr, 0, font_extents.height);
 
-		hb_buffer_t *buffer = entry->backend.hb_buffer;
-
 		hb_buffer_clear_contents(buffer);
 		setup_hb_buffer(buffer);
-		if (i < entry->results.count) {
-			hb_buffer_add_utf8(buffer, entry->results.buf[i], -1, 0, -1);
-			hb_shape(entry->backend.hb_font, buffer, NULL, 0);
-			render_hb_buffer(cr, buffer, entry->image.scale);
-		}
+		hb_buffer_add_utf8(buffer, entry->results.buf[i], -1, 0, -1);
+		hb_shape(entry->backend.hb_font, buffer, NULL, 0);
+		render_hb_buffer(cr, buffer, entry->image.scale);
 	}
 }