correctly display single line selection

src/main.odin

@@ -168,9 +168,54 @@ main :: proc() {
 			}
 			raw_data(line)[len(line)] = 0
 
-			cstr := strings.unsafe_string_to_cstring(string(line[:]))
-			pos := r.Vector2{0, font_size * f32(line_index)}
-			r.DrawTextEx(font, cstr, pos, font_size, 0, r.WHITE)
+
+			if selection.active &&
+			   line_index == selection.start_line &&
+			   line_index == selection.end_line {
+				selection_begin := min(selection.start_char, selection.end_char)
+				selection_end := max(selection.start_char, selection.end_char)
+				prefix := line[:selection_begin]
+				suffix := line[selection_end + 1:] if selection_end + 1 < len(line) else []u8{}
+				// need to copy these into separate buffers for zero value
+				x: f32 = 0.0
+				if len(prefix) != 0 {
+					cstr := strings.clone_to_cstring(string(prefix), context.temp_allocator)
+					measurements := r.MeasureTextEx(font, cstr, font_size, 0)
+					pos := r.Vector2{x, font_size * f32(line_index)}
+					r.DrawTextEx(font, cstr, pos, font_size, 0, r.WHITE)
+					x += measurements.x
+				}
+
+				selected_str := string(line[selection_begin:selection_end + 1])
+				cstr :=
+					strings.clone_to_cstring(selected_str, context.temp_allocator) if len(suffix) != 0 else strings.unsafe_string_to_cstring(selected_str)
+				measurements := r.MeasureTextEx(font, cstr, font_size, 0)
+				pos := r.Vector2{x, font_size * f32(line_index)}
+				r.DrawRectangle(
+					i32(pos.x),
+					i32(pos.y),
+					i32(measurements.x),
+					i32(measurements.y),
+					r.WHITE,
+				)
+				r.DrawTextEx(font, cstr, pos, font_size, 0, r.BLACK)
+				x += measurements.x
+
+				if len(suffix) != 0 {
+					cstr := strings.unsafe_string_to_cstring(string(suffix))
+					// cstr := strings.clone_to_cstring(string(suffix), context.temp_allocator)
+					pos := r.Vector2{x, font_size * f32(line_index)}
+					r.DrawTextEx(font, cstr, pos, font_size, 0, r.WHITE)
+				}
+			} else if selection.active && line_index == selection.start_line {
+			} else if selection.active && line_index == selection.end_line {
+			} else if selection.active && selection.start_line < line_index && line_index < selection.end_line {
+			} else {
+				// No selection active
+				cstr := strings.unsafe_string_to_cstring(string(line[:]))
+				pos := r.Vector2{0, font_size * f32(line_index)}
+				r.DrawTextEx(font, cstr, pos, font_size, 0, r.WHITE)
+			}
 		}
 
 		render_cursor(&cursor)