[rtext] Fix GetCodepointNext() to return default value on invalid inp…

…ut 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>

src/rtext.c

@@ -1071,10 +1071,6 @@ void DrawTextEx(Font font, const char *text, Vector2 position, float fontSize, f
  int codepoint = GetCodepointNext(&text[i], &codepointByteCount);
  int index = GetGlyphIndex(font, codepoint);
 
- // 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
@@ -1205,18 +1201,15 @@ Vector2 MeasureTextEx(Font font, const char *text, float fontSize, float spacing
  int letter = 0; // Current character
  int index = 0; // Index position in sprite font
 
- for (int i = 0; i < size; i++)
+ for (int i = 0; i < size;)
  {
  byteCounter++;
 
  int next = 0;
  letter = GetCodepointNext(&text[i], &next);
  index = GetGlyphIndex(font, letter);
 
- // 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 so to not skip any we set next = 1
- if (letter == 0x3f) next = 1;
- i += next - 1;
+ i += next;
 
  if (letter != '\n')
  {
@@ -1734,8 +1727,7 @@ int GetCodepointCount(const char *text)
  int next = 0;
  int letter = GetCodepointNext(ptr, &next);
 
- if (letter == 0x3f) ptr += 1;
- else ptr += next;
+ ptr += next;
 
  length++;
  }
@@ -1896,28 +1888,31 @@ int GetCodepointNext(const char *text, int *codepointSize)
 {
  const char *ptr = text;
  int codepoint = 0x3f; // Codepoint (defaults to '?')
- *codepointSize = 0;
+ *codepointSize = 1;
 
  // Get current codepoint and bytes processed
  if (0xf0 == (0xf8 & ptr[0]))
  {
  // 4 byte UTF-8 codepoint
+ if(((ptr[1] & 0xC0) ^ 0x80) || ((ptr[2] & 0xC0) ^ 0x80) || ((ptr[3] & 0xC0) ^ 0x80)) { return codepoint; } //10xxxxxx checks
  codepoint = ((0x07 & ptr[0]) << 18) | ((0x3f & ptr[1]) << 12) | ((0x3f & ptr[2]) << 6) | (0x3f & ptr[3]);
  *codepointSize = 4;
  }
  else if (0xe0 == (0xf0 & ptr[0]))
  {
  // 3 byte UTF-8 codepoint */
+ if(((ptr[1] & 0xC0) ^ 0x80) || ((ptr[2] & 0xC0) ^ 0x80)) { return codepoint; } //10xxxxxx checks
  codepoint = ((0x0f & ptr[0]) << 12) | ((0x3f & ptr[1]) << 6) | (0x3f & ptr[2]);
  *codepointSize = 3;
  }
  else if (0xc0 == (0xe0 & ptr[0]))
  {
  // 2 byte UTF-8 codepoint
+ if((ptr[1] & 0xC0) ^ 0x80) { return codepoint; } //10xxxxxx checks
  codepoint = ((0x1f & ptr[0]) << 6) | (0x3f & ptr[1]);
  *codepointSize = 2;
  }
- else
+ else if (0x00 == (0x80 & ptr[0]))
  {
  // 1 byte UTF-8 codepoint
  codepoint = ptr[0];

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