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

3 files changed, 31 insertions, 6 deletions

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;
+}