Attempt to fix font glyph texture overlap by aligning texture size to

next character size

Add function to get the start of a utf8 codepoint (backwards), test utf8
functions

6 files changed, 66 insertions, 7 deletions

diff --git a/include/mgl/graphics/font.h b/include/mgl/graphics/font.h
index adcc8a7..6b7eb34 100644
--- a/include/mgl/graphics/font.h
+++ b/include/mgl/graphics/font.h
@@ -25,7 +25,7 @@ typedef struct {
 } mgl_font_atlas;
 
 struct mgl_font {
-    mgl_texture texture;
+    mgl_texture texture; /* Font texture coordinates are in pixel space */
     mgl_font_atlas font_atlas;
     unsigned int character_size;
     mgl_font_char_map char_map;
diff --git a/include/mgl/system/utf8.h b/include/mgl/system/utf8.h
index 7120f1a..794884d 100644
--- a/include/mgl/system/utf8.h
+++ b/include/mgl/system/utf8.h
@@ -9,6 +9,13 @@
     Returns false on failure. |decoded_codepoint| is set to |str[0]| if size > 0 and |codepoint_length| is set to 1
 */
 bool mgl_utf8_decode(const unsigned char *str, size_t size, uint32_t *decoded_codepoint, size_t *codepoint_length);
+/*
+    |str| should be the start of the utf8 string and |size| is the size of the string.
+    Returns the index of the start of the codepoint that starts at or before |offset|,
+    or if the string contains invalid utf8 then the index to the invalid character is returned.
+    Returns 0 if start of codepoint is not found.
+*/
+size_t mgl_utf8_get_start_of_codepoint(const unsigned char *str, size_t size, size_t offset);
 
 #endif /* MGL_UTF8_H */
 
diff --git a/src/graphics/font.c b/src/graphics/font.c
index 0044d96..f73c023 100644
--- a/src/graphics/font.c
+++ b/src/graphics/font.c
@@ -4,8 +4,6 @@
 #define STB_TRUETYPE_IMPLEMENTATION
 #include "../../external/stb_truetype.h"
 
-/* TODO: Use correct atlas padding after resize. Its incorrect because padding from previous size doesn't accumulate */
-
 /* Need padding so filtering doesn't touch pixels in another glyphs area */
 #define GLYPH_PADDING 2
 #define GLYPH_UPSAMPLE 1
@@ -57,6 +55,14 @@ void mgl_font_unload(mgl_font *self) {
     self->font_info = NULL;
 }
 
+static int align_up_to_next_value_of(int value, int alignment) {
+    int offset_to_next_alignment = value % alignment;
+    if(offset_to_next_alignment == 0)
+        return value;
+    else
+        return value + (alignment - offset_to_next_alignment);
+}
+
 static void mgl_font_handle_new_render_position(mgl_font *self, int glyph_width) {
     if(self->font_atlas.pointer_position.x + glyph_width + GLYPH_PADDING >= self->font_atlas.width) {
         if(self->font_atlas.pointer_position.y + self->current_line_max_height + GLYPH_PADDING >= self->font_atlas.height && self->font_atlas.render_section != MGL_ATLAS_SECTION_RIGHT) {
@@ -87,8 +93,8 @@ static void mgl_font_handle_new_render_position(mgl_font *self, int glyph_width)
             if(mgl_texture_resize(&self->texture, self->font_atlas.width * 2, self->font_atlas.height * 2, NULL) == 0) {
                 self->font_atlas.prev_width = self->font_atlas.width;
                 self->font_atlas.prev_height = self->font_atlas.height;
-                self->font_atlas.width *= 2;
-                self->font_atlas.height *= 2;
+                self->font_atlas.width = align_up_to_next_value_of(self->font_atlas.width * 2, self->character_size);
+                self->font_atlas.height = align_up_to_next_value_of(self->font_atlas.height * 2, self->character_size);
 
                 self->font_atlas.render_section = MGL_ATLAS_SECTION_RIGHT;
                 self->font_atlas.pointer_position.x = self->font_atlas.prev_width;
@@ -99,6 +105,7 @@ static void mgl_font_handle_new_render_position(mgl_font *self, int glyph_width)
                 mgl_font_glyph glyph_dummy;
                 mgl_font_char_iterator font_char_it = mgl_font_char_map_begin(&self->char_map);
                 while(font_char_it.value) {
+                    /* TODO: Update glyph without calling this, since this needs to get glyph from hash map again */
                     mgl_font_get_glyph(self, font_char_it.value->key, &glyph_dummy);
                     mgl_font_char_iterator_next(&font_char_it);
                 }
@@ -108,7 +115,7 @@ static void mgl_font_handle_new_render_position(mgl_font *self, int glyph_width)
         } else if(self->font_atlas.render_section == MGL_ATLAS_SECTION_RIGHT && self->font_atlas.pointer_position.y + self->current_line_max_height + GLYPH_PADDING >= self->font_atlas.prev_height) {
             self->font_atlas.render_section = MGL_ATLAS_SECTION_BOTTOM;
             self->font_atlas.pointer_position.x = GLYPH_PADDING;
-            self->font_atlas.pointer_position.y = self->font_atlas.prev_height;
+            self->font_atlas.pointer_position.y += self->current_line_max_height + GLYPH_PADDING;
         } else {
             if(self->font_atlas.render_section != MGL_ATLAS_SECTION_RIGHT) {
                 self->font_atlas.pointer_position.x = GLYPH_PADDING;
@@ -123,7 +130,7 @@ static void mgl_font_handle_new_render_position(mgl_font *self, int glyph_width)
 
 int mgl_font_get_glyph(mgl_font *self, uint32_t codepoint, mgl_font_glyph *glyph) {
     if(self->font_atlas.width == 0) {
-        const int initial_atlas_size = 128;
+        const int initial_atlas_size = align_up_to_next_value_of(128, self->character_size);
         /* TODO: Scale by character size */
         mgl_texture_load_options load_options = {
             .compressed = false,
diff --git a/src/graphics/font_char_map.c b/src/graphics/font_char_map.c
index abaa56a..64c4674 100644
--- a/src/graphics/font_char_map.c
+++ b/src/graphics/font_char_map.c
@@ -12,6 +12,7 @@
 #error Unsupported system. Only systems where a pointer is 32-bits or 64-bits are supported.
 #endif
 
+/* |align| should be a multiple of 2 */
 static size_t align_to(size_t value, size_t align) {
     const size_t is_aligned = (value & (align - 1));
     if(is_aligned == 0) {
diff --git a/src/system/utf8.c b/src/system/utf8.c
index 201fedf..5d5ec79 100644
--- a/src/system/utf8.c
+++ b/src/system/utf8.c
@@ -73,3 +73,20 @@ bool mgl_utf8_decode(const unsigned char *str, size_t size, uint32_t *decoded_co
     *decoded_codepoint = codepoint;
     return true;
 }
+
+/* TODO: Optimize (remove branching, etc) */
+size_t mgl_utf8_get_start_of_codepoint(const unsigned char *str, size_t size, size_t offset) {
+    if(size == 0)
+        return 0;
+
+    if(offset > size - 1)
+        offset = size - 1;
+
+    /* i <= offset is an overflow (underflow?) check */
+    for(size_t i = offset; i <= offset; --i) {
+        if((str[i] & 0xC0) != 0x80)
+            return i;
+    }
+
+    return 0;
+}
diff --git a/tests/main.c b/tests/main.c
index cee3ec7..b341bb3 100644
--- a/tests/main.c
+++ b/tests/main.c
@@ -13,6 +13,7 @@
 #include <mgl/graphics/shader.h>
 #include <mgl/system/clock.h>
 #include <mgl/system/fileutils.h>
+#include <mgl/system/utf8.h>
 
 #define require_equals(a, b) do { if((a) != (b)) { fprintf(stderr, "Assert failed on line %d: %s == %s\n", __LINE__, #a, #b); abort(); } } while(0)
 #define require_not_equals(a, b) do { if((a) == (b)) { fprintf(stderr, "Assert failed on line %d: %s != %s\n", __LINE__, #a, #b); abort(); } } while(0)
@@ -189,8 +190,34 @@ static void test_hash_map() {
     mgl_font_char_map_deinit(&char_map);
 }
 
+static void test_utf8() {
+    uint32_t codepoint = 0;
+    size_t codepoint_length = 0;
+
+    require_equals(mgl_utf8_decode("a", 1, &codepoint, &codepoint_length), true);
+    require_equals(codepoint, 0x61);
+    require_equals(codepoint_length, 1);
+
+    require_equals(mgl_utf8_decode("á", 2, &codepoint, &codepoint_length), true);
+    require_equals(codepoint, 0xE1);
+    require_equals(codepoint_length, 2);
+
+    require_equals(mgl_utf8_decode("‡", 3, &codepoint, &codepoint_length), true);
+    require_equals(codepoint, 0x2021);
+    require_equals(codepoint_length, 3);
+
+    require_equals(mgl_utf8_decode("𒀀", 4, &codepoint, &codepoint_length), true);
+    require_equals(codepoint, 0x12000);
+    require_equals(codepoint_length, 4);
+
+    require_equals(mgl_utf8_get_start_of_codepoint("abc", 3, 0), 0);
+    require_equals(mgl_utf8_get_start_of_codepoint("abc", 3, 2), 2);
+    require_equals(mgl_utf8_get_start_of_codepoint("abö", 3, 4), 2);
+}
+
 int main(int argc, char **argv) {
     test_hash_map();
+    test_utf8();
 
     if(mgl_init() != 0)
         return 1;