[rtext] Fix GetCodepointNext() to return default value on invalid input with size=0 (#2997)

* Fix GetCodepointNext to return default value with size=0 on invalid input. Modify LoadCodepoints to work when GetCodepointNext returns a size of 0. All internal use of GetCodepointNext and GetCodepointPrev checked. This fix may break external code dealing with invalid input as the old code erroneously never returned a size of 0, external code that doesn't properly check for size=0 may endlessly loop or overflow a buffer on invalid input.

* Change default behaviour of GetCodepointNext to return a size of 1 instead of 0. This matches existing prod behaviour and guarantees size 1..4 is returned. Simplify internal code that uses GetCodepointNext that previously had to account for size=0.

* Simplified progressing through a UTF-8 string in ImageTextEx and MeasureTextEx. This change matches existing precedent in DrawTextEx

* GetCodepointNext: Add 10xxxxxx checks to multibyte encodings.

---------

Co-authored-by: anon <anon>

1 files changed, 2 insertions, 6 deletions

diff --git a/src/rtextures.c b/src/rtextures.c
index fb63f2ff..bd652e6b 100644
--- a/src/rtextures.c
+++ b/src/rtextures.c
@@ -1266,17 +1266,13 @@ Image ImageTextEx(Font font, const char *text, float fontSize, float spacing, Co
     // Create image to store text
     imText = GenImageColor((int)imSize.x, (int)imSize.y, BLANK);
 
-    for (int i = 0; i < size; i++)
+    for (int i = 0; i < size;)
     {
         // Get next codepoint from byte string and glyph index in font
         int codepointByteCount = 0;
         int codepoint = GetCodepointNext(&text[i], &codepointByteCount);    // WARNING: Module required: rtext
         int index = GetGlyphIndex(font, codepoint);                         // WARNING: Module required: rtext
 
-        // NOTE: Normally we exit the decoding sequence as soon as a bad byte is found (and return 0x3f)
-        // but we need to draw all the bad bytes using the '?' symbol moving one byte
-        if (codepoint == 0x3f) codepointByteCount = 1;
-
         if (codepoint == '\n')
         {
             // NOTE: Fixed line spacing of 1.5 line-height
@@ -1296,7 +1292,7 @@ Image ImageTextEx(Font font, const char *text, float fontSize, float spacing, Co
             else textOffsetX += font.glyphs[index].advanceX + (int)spacing;
         }
 
-        i += (codepointByteCount - 1);   // Move text bytes counter to next codepoint
+        i += codepointByteCount;   // Move text bytes counter to next codepoint
     }
 
     // Scale image depending on text size