[Bindings/Odin] Improve example text measurement function (#541)

Author: rats159

bindings/odin/examples/clay-official-website/clay_renderer_raylib.odin

@@ -1,5 +1,7 @@
 package main
 
+import "core:unicode/utf8"
+import "base:runtime"
 import clay "../../clay-odin"
 import "core:math"
 import "core:strings"
@@ -16,24 +18,74 @@ clay_color_to_rl_color :: proc(color: clay.Color) -> rl.Color {
 
 raylib_fonts := [dynamic]Raylib_Font{}
 
-measure_text :: proc "c" (text: clay.StringSlice, config: ^clay.TextElementConfig, userData: rawptr) -> clay.Dimensions {
-    line_width: f32 = 0
+// Alias for compatibility, default to ascii support
+measure_text :: measure_text_ascii
 
-    font := raylib_fonts[config.fontId].font
+measure_text_unicode :: proc "c" (text: clay.StringSlice, config: ^clay.TextElementConfig, userData: rawptr) -> clay.Dimensions {
+    // Needed for grapheme_count
+    context = runtime.default_context()
+    
+	line_width: f32 = 0
+    
+	font := raylib_fonts[config.fontId].font
+	text_str := string(text.chars[:text.length])
 
-    for i in 0 ..< text.length {
-        glyph_index := text.chars[i] - 32
+    // This function seems somewhat expensive, if you notice performance issues, you could assume
+    // - 1 codepoint per visual character (no grapheme clusters), where you can get the length from the loop
+    // - 1 byte per visual character (ascii), where you can get the length with `text.length`
+    // see `measure_text_ascii`
+    grapheme_count, _, _ := utf8.grapheme_count(text_str)
+
+	for letter, byte_idx in text_str {
+		glyph_index := rl.GetGlyphIndex(font, letter)
 
         glyph := font.glyphs[glyph_index]
 
-        if glyph.advanceX != 0 {
-            line_width += f32(glyph.advanceX)
-        } else {
-            line_width += font.recs[glyph_index].width + f32(glyph.offsetX)
-        }
-    }
+		if glyph.advanceX != 0 {
+			line_width += f32(glyph.advanceX)
+		} else {
+			line_width += font.recs[glyph_index].width + f32(font.glyphs[glyph_index].offsetX)
+		}
+	}
+
+	scaleFactor := f32(config.fontSize) / f32(font.baseSize)
+
+    // Note: 
+    //   I'd expect this to be `grapheme_count - 1`, 
+    //   but that seems to be one letterSpacing too small
+    //   maybe that's a raylib bug, maybe that's Clay?
+	total_spacing := f32(grapheme_count) * f32(config.letterSpacing)
+
+	return {width = line_width * scaleFactor + total_spacing, height = f32(config.fontSize)}
+}
+
+measure_text_ascii :: proc "c" (text: clay.StringSlice, config: ^clay.TextElementConfig, userData: rawptr) -> clay.Dimensions {    
+	line_width: f32 = 0
+    
+	font := raylib_fonts[config.fontId].font
+	text_str := string(text.chars[:text.length])
+
+	for i in 0..<len(text_str) {
+		glyph_index := text_str[i] - 32
+
+        glyph := font.glyphs[glyph_index]
+
+		if glyph.advanceX != 0 {
+			line_width += f32(glyph.advanceX)
+		} else {
+			line_width += font.recs[glyph_index].width + f32(font.glyphs[glyph_index].offsetX)
+		}
+	}
+
+	scaleFactor := f32(config.fontSize) / f32(font.baseSize)
+
+    // Note: 
+    //   I'd expect this to be `len(text_str) - 1`, 
+    //   but that seems to be one letterSpacing too small
+    //   maybe that's a raylib bug, maybe that's Clay?
+	total_spacing := f32(len(text_str)) * f32(config.letterSpacing)
 
-    return {width = line_width / 2, height = f32(config.fontSize)}
+	return {width = line_width * scaleFactor + total_spacing, height = f32(config.fontSize)}
 }
 
 clay_raylib_render :: proc(render_commands: ^clay.ClayArray(clay.RenderCommand), allocator := context.temp_allocator) {