Interpret invalid glyphs as zero-width placeholder

As some variations of Path of Building let UTF-8 into strings there is
the possibility of reading out of bounds in the array of glyphs for
string measurement as characters larger than 128 are either after or
before the array of glyphs.

To satisfy the Unicode detection logic recently added to the Lua app
this needs to either produce placeholder widths of zero or greater than
100. This implementation makes the conservative choice of zero width.

Author: zao

engine/render/r_font.cpp

@@ -32,6 +32,14 @@ struct f_fontHeight_s {
 	int		height;
 	int		numGlyph;
 	f_glyph_s glyphs[128];
+	f_glyph_s defGlyph{0.0, 0.0, 0.0, 0.0, 0, 0, 0};
+
+	f_glyph_s const& Glyph(char ch) const {
+		if ((unsigned char)ch >= numGlyph) {
+			return defGlyph;
+		}
+		return glyphs[(unsigned char)ch];
+	}
 };
 
 // ===========
@@ -126,11 +134,13 @@ int r_font_c::StringWidthInternal(f_fontHeight_s* fh, const char* str)
 		if (escLen) {
 			str+= escLen;
 		} else if (*str == '\t') {
-			int spWidth = fh->glyphs[' '].width + fh->glyphs[' '].spLeft + fh->glyphs[' '].spRight;
-			width+= spWidth << 2;
+			auto& glyph = fh->Glyph(' ');
+			int spWidth = glyph.width + glyph.spLeft + glyph.spRight;
+			width += spWidth << 2;
 			str++;
 		} else {
-			width+= fh->glyphs[*str].width + fh->glyphs[*str].spLeft + fh->glyphs[*str].spRight;
+			auto& glyph = fh->Glyph(*str);
+			width+= glyph.width + glyph.spLeft + glyph.spRight;
 			str++;
 		}
 	}
@@ -165,15 +175,17 @@ const char* r_font_c::StringCursorInternal(f_fontHeight_s* fh, const char* str,
 		if (escLen) {
 			str+= escLen;
 		} else if (*str == '\t') {
-			int spWidth = fh->glyphs[' '].width + fh->glyphs[' '].spLeft + fh->glyphs[' '].spRight;
+			auto& glyph = fh->Glyph(' ');
+			int spWidth = glyph.width + glyph.spLeft + glyph.spRight;
 			x+= spWidth << 1;
 			if (curX <= x) {
 				break;
 			}
 			x+= spWidth << 1;
 			str++;
 		} else {
-			x+= fh->glyphs[*str].width + fh->glyphs[*str].spLeft + fh->glyphs[*str].spRight;
+			auto& glyph = fh->Glyph(*str);
+			x+= glyph.width + glyph.spLeft + glyph.spRight;
 			if (curX <= x) {
 				break;
 			}
@@ -274,28 +286,29 @@ void r_font_c::DrawTextLine(scp_t pos, int align, int height, col4_t col, const
 
 		// Handle tabs
 		if (*str == '\t') {
-			int spWidth = fh->glyphs[' '].width + fh->glyphs[' '].spLeft + fh->glyphs[' '].spRight;
+			auto& glyph = fh->Glyph(' ');
+			int spWidth = glyph.width + glyph.spLeft + glyph.spRight;
 			x+= (spWidth << 2) * scale;
 			str++;
 			continue;
 		}
 
 		// Draw glyph
-		f_glyph_s* glyph = fh->glyphs + *(str++);
-		x+= glyph->spLeft * scale;
-		if (glyph->width) {
-			double w = glyph->width * scale;
+		auto& glyph = fh->Glyph(*str++);
+		x+= glyph.spLeft * scale;
+		if (glyph.width) {
+			double w = glyph.width * scale;
 			if (x + w >= 0 && x < renderer->VirtualScreenWidth()) {
 				renderer->curLayer->Quad(
-					glyph->tcLeft, glyph->tcTop, x, y,
-					glyph->tcRight, glyph->tcTop, x + w, y,
-					glyph->tcRight, glyph->tcBottom, x + w, y + height,
-					glyph->tcLeft, glyph->tcBottom, x, y + height
+					glyph.tcLeft, glyph.tcTop, x, y,
+					glyph.tcRight, glyph.tcTop, x + w, y,
+					glyph.tcRight, glyph.tcBottom, x + w, y + height,
+					glyph.tcLeft, glyph.tcBottom, x, y + height
 				);
 			}
 			x+= w;
 		}
-		x+= glyph->spRight * scale;
+		x+= glyph.spRight * scale;
 	}
 }