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Fixed bug 4351 - Fixing corner case with underline / strike-through
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Sylvain

When applying small size and big outline and underline and strike through, it happens nasty corner cases.
that would make the code crash if there were not boundary check.


- we have already increased the limit for underline style set by something like this:
 font->height = SDL_max(font->height, bottom_row);

I added the same update of font->height also for strike-through.
(big outline makes the lines thickness be greater than height/2 and then bottom_row writes than surface height).

- Then now, there is a circular dependency, because:
  TTF_strikethrough_top_row() returns (height/2)
  bottom_row = TTF_strikethrough_top_row() + thickness
  new height is SDL_max(font->height, bottom_row);
  when it renders, TTF_strikethrough_top_row() returns (new_height/2). which can write out of bounds.

So I just move the strike/underline_to_row in the font structure. They are initialized when style changes.
And not recomputed any more each time it renders.


We just need to make sure the TTF_Size() is set correctly. Since the line can be of any thickness.
it's inside a boundary box of miny=0 maxy=font->height at yoffset 0.
We can virtually treat it as glyph by adding the same check:
  maxy = SDL_max(maxy, glyph->yoffset + glyph->maxy - glyph->miny);
ie
  maxy = SDL_max(maxy, font->height);
finally simply initializing
  maxy = font->height;

and also the height surface
  *h = SDL_max(font->height, maxy - miny);
as maxy >= font->height, and miny <=0, becames only:
  *h = (maxy - miny);


In the modification:
- create underline/strikethrough_top_row into TTF_FONT structure, and remove TTF_underline/strikethrough_top_row() private functions.
- remove the boundary check of DrawLines
- merge together TTF_drawLine_Solid() & TTF_drawLine_Shaded() as there are similar. (color 1, vers NUMGRAY - 1)
- inline TTF_initLineMectrics just initializing two vars.
- remove a duplicate "maxx = SDL_max(maxx, x + glyph->advance);"
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@slouken
slouken committed Nov 2, 2018
1 parent 50aa8c9 commit 26462be
Showing 1 changed file with 43 additions and 77 deletions.
120 changes: 43 additions & 77 deletions SDL_ttf.c
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Expand Up @@ -91,6 +91,9 @@ struct _TTF_Font {
int underline_offset;
int underline_height;

int underline_top_row;
int strikethrough_top_row;

/* Cache for style-transformed glyphs */
c_glyph *current;
c_glyph cache[257]; /* 257 is a prime */
Expand Down Expand Up @@ -136,74 +139,30 @@ static int TTF_byteswapped = 0;

static int TTF_initFontMetrics(TTF_Font* font);

/* Gets the top row of the underline. */
static int TTF_underline_top_row(TTF_Font *font)
{
return font->ascent - font->underline_offset - 1;
}

/* Gets the top row of the strikethrough */
static int TTF_strikethrough_top_row(TTF_Font *font)
{
return font->height / 2;
}

static void TTF_initLineMectrics(const TTF_Font *font, const SDL_Surface *textbuf, const int row, Uint8 **pdst, int *pheight)
{
*pdst = (Uint8 *)textbuf->pixels + row * textbuf->pitch;
*pheight = font->underline_height;
}

/* Draw a solid line of underline_height at the given row. */
static void TTF_drawLine_Solid(const TTF_Font *font, const SDL_Surface *textbuf, const int row)
{
int line;
Uint8 *dst_check = (Uint8*)textbuf->pixels + textbuf->pitch * textbuf->h;
Uint8 *dst;
int height;

TTF_initLineMectrics(font, textbuf, row, &dst, &height);

/* Draw line */
for (line=height; line>0 && dst < dst_check; --line) {
/* 1 because 0 is the bg color */
SDL_memset(dst, 1, textbuf->w);
dst += textbuf->pitch;
}
}

/* Draw a shaded line of underline_height at the given row. */
static void TTF_drawLine_Shaded(const TTF_Font *font, const SDL_Surface *textbuf, const int row)
/* Draw a solid or shaded line of underline_height at the given row. */
static void TTF_drawLine(const TTF_Font *font, const SDL_Surface *textbuf, int row, int color)
{
int line;
Uint8 *dst_check = (Uint8*)textbuf->pixels + textbuf->pitch * textbuf->h;
Uint8 *dst;
int height;

TTF_initLineMectrics(font, textbuf, row, &dst, &height);
Uint8 *dst = (Uint8 *)textbuf->pixels + row * textbuf->pitch;

/* Draw line */
for (line=height; line>0 && dst < dst_check; --line) {
SDL_memset(dst, NUM_GRAYS - 1, textbuf->w);
for (line = font->underline_height; line > 0; --line) {
SDL_memset(dst, color, textbuf->w);
dst += textbuf->pitch;
}
}

/* Draw a blended line of underline_height */
static void TTF_drawLine_Blended(const TTF_Font *font, const SDL_Surface *textbuf, const int row, const int line_width, const Uint32 color)
static void TTF_drawLine_Blended(const TTF_Font *font, const SDL_Surface *textbuf, int row, int line_width, Uint32 color)
{
int line;
Uint32 *dst_check = (Uint32*)textbuf->pixels + textbuf->pitch/4 * textbuf->h;
Uint32 *dst;
int height;
Uint32 *dst = (Uint32 *)textbuf->pixels + row * textbuf->pitch/4;
int col;
Uint32 pixel = color | 0xFF000000; /* Amask */

TTF_initLineMectrics(font, textbuf, row, (Uint8**) &dst, &height);

/* Draw line */
for (line=height; line>0 && dst < dst_check; --line) {
for (col=0; col < line_width; ++col) {
for (line = font->underline_height; line > 0; --line) {
for (col = 0; col < line_width; ++col) {
dst[col] = pixel;
}
dst += textbuf->pitch/4;
Expand Down Expand Up @@ -485,9 +444,17 @@ static int TTF_initFontMetrics(TTF_Font* font)
font->ascent += 2 * fo;
}

font->underline_top_row = font->ascent - font->underline_offset - 1;
font->strikethrough_top_row = font->height / 2;

/* Update height according to the needs of the underline style */
if (TTF_HANDLE_STYLE_UNDERLINE(font)) {
int bottom_row = TTF_underline_top_row(font) + font->underline_height;
int bottom_row = font->underline_top_row + font->underline_height;
font->height = SDL_max(font->height, bottom_row);
}
/* Update height according to the needs of the strikethrough style */
if (TTF_HANDLE_STYLE_STRIKETHROUGH(font)) {
int bottom_row = font->strikethrough_top_row + font->underline_height;
font->height = SDL_max(font->height, bottom_row);
}

Expand All @@ -500,7 +467,7 @@ static int TTF_initFontMetrics(TTF_Font* font)
printf("\tunderline_offset = %d, underline_height = %d\n",
font->underline_offset, font->underline_height);
printf("\tunderline_top_row = %d, strikethrough_top_row = %d\n",
TTF_underline_top_row(font), TTF_strikethrough_top_row(font));
font->underline_top_row, font->strikethrough_top_row);
#endif

font->glyph_overhang = face->size->metrics.y_ppem / 10;
Expand Down Expand Up @@ -554,7 +521,6 @@ static void Flush_Cache(TTF_Font* font)
if (font->cache[i].cached) {
Flush_Glyph(&font->cache[i]);
}

}
}

Expand Down Expand Up @@ -880,11 +846,10 @@ static FT_Error Load_Glyph(TTF_Font* font, Uint32 ch, c_glyph* cached, int want)
{
int width_max = SDL_max(cached->advance, cached->maxx - cached->minx);
int rows_max = SDL_max(font->height, cached->maxy - cached->miny);

dst->width = SDL_min((int)dst->width, width_max);
dst->rows = SDL_min((int)dst->rows, rows_max);
}

}

/* We're done, mark this glyph cached */
Expand Down Expand Up @@ -1149,7 +1114,7 @@ char *TTF_FontFaceStyleName(const TTF_Font *font)

int TTF_GlyphIsProvided(const TTF_Font *font, Uint16 ch)
{
return FT_Get_Char_Index(font->face, ch);
return FT_Get_Char_Index(font->face, ch);
}

int TTF_GlyphMetrics(TTF_Font *font, Uint16 ch,
Expand Down Expand Up @@ -1211,6 +1176,8 @@ static int TTF_SizeUTF8_Internal(TTF_Font *font, const char *text, int *w, int *

TTF_CHECKPOINTER(text, -1);

maxy = font->height;

/* Load each character and sum it's bounding box */
textlen = SDL_strlen(text);
while (textlen > 0) {
Expand All @@ -1235,7 +1202,6 @@ static int TTF_SizeUTF8_Internal(TTF_Font *font, const char *text, int *w, int *

minx = SDL_min(minx, x + glyph->minx);

maxx = SDL_max(maxx, x + glyph->advance);
maxx = SDL_max(maxx, x + glyph->maxx);
maxx = SDL_max(maxx, x + glyph->advance);

Expand All @@ -1262,7 +1228,7 @@ static int TTF_SizeUTF8_Internal(TTF_Font *font, const char *text, int *w, int *
*w = (maxx - minx);
}
if (h) {
*h = SDL_max(font->height, maxy - miny);
*h = (maxy - miny);
}
return 0;
}
Expand Down Expand Up @@ -1390,14 +1356,14 @@ SDL_Surface *TTF_RenderUTF8_Solid(TTF_Font *font,

/* Handle the underline style */
if (TTF_HANDLE_STYLE_UNDERLINE(font)) {
row = TTF_underline_top_row(font);
TTF_drawLine_Solid(font, textbuf, row + ystart);
int first_row = font->underline_top_row + ystart;
TTF_drawLine(font, textbuf, first_row, 1 /* 1 because 0 is the bg color */ );
}

/* Handle the strikethrough style */
if (TTF_HANDLE_STYLE_STRIKETHROUGH(font)) {
row = TTF_strikethrough_top_row(font);
TTF_drawLine_Solid(font, textbuf, row + ystart);
int first_row = font->strikethrough_top_row + ystart;
TTF_drawLine(font, textbuf, first_row, 1 /* 1 because 0 is the bg color */ );
}
return textbuf;
}
Expand Down Expand Up @@ -1554,14 +1520,14 @@ SDL_Surface *TTF_RenderUTF8_Shaded(TTF_Font *font,

/* Handle the underline style */
if (TTF_HANDLE_STYLE_UNDERLINE(font)) {
row = TTF_underline_top_row(font);
TTF_drawLine_Shaded(font, textbuf, row + ystart);
int first_row = font->underline_top_row + ystart;
TTF_drawLine(font, textbuf, first_row, NUM_GRAYS - 1);
}

/* Handle the strikethrough style */
if (TTF_HANDLE_STYLE_STRIKETHROUGH(font)) {
row = TTF_strikethrough_top_row(font);
TTF_drawLine_Shaded(font, textbuf, row + ystart);
int first_row = font->strikethrough_top_row + ystart;
TTF_drawLine(font, textbuf, first_row, NUM_GRAYS - 1);
}
return textbuf;
}
Expand Down Expand Up @@ -1712,14 +1678,14 @@ SDL_Surface *TTF_RenderUTF8_Blended(TTF_Font *font,

/* Handle the underline style */
if (TTF_HANDLE_STYLE_UNDERLINE(font)) {
row = TTF_underline_top_row(font);
TTF_drawLine_Blended(font, textbuf, row + ystart, textbuf->w, pixel | (Uint32)fg.a << 24);
int first_row = font->underline_top_row + ystart;
TTF_drawLine_Blended(font, textbuf, first_row, textbuf->w, pixel | (Uint32)fg.a << 24);
}

/* Handle the strikethrough style */
if (TTF_HANDLE_STYLE_STRIKETHROUGH(font)) {
row = TTF_strikethrough_top_row(font);
TTF_drawLine_Blended(font, textbuf, row + ystart, textbuf->w, pixel | (Uint32)fg.a << 24);
int first_row = font->strikethrough_top_row + ystart;
TTF_drawLine_Blended(font, textbuf, first_row, textbuf->w, pixel | (Uint32)fg.a << 24);
}
return textbuf;
}
Expand Down Expand Up @@ -1983,14 +1949,14 @@ SDL_Surface *TTF_RenderUTF8_Blended_Wrapped(TTF_Font *font,

/* Handle the underline style */
if (TTF_HANDLE_STYLE_UNDERLINE(font)) {
row = TTF_underline_top_row(font);
TTF_drawLine_Blended(font, textbuf, rowHeight * line + row + ystart, SDL_min(line_width, textbuf->w), pixel | (Uint32)fg.a << 24);
int first_row = rowHeight * line + font->underline_top_row + ystart;
TTF_drawLine_Blended(font, textbuf, first_row, SDL_min(line_width, textbuf->w), pixel | (Uint32)fg.a << 24);
}

/* Handle the strikethrough style */
if (TTF_HANDLE_STYLE_STRIKETHROUGH(font)) {
row = TTF_strikethrough_top_row(font);
TTF_drawLine_Blended(font, textbuf, rowHeight * line + row + ystart, SDL_min(line_width, textbuf->w), pixel | (Uint32)fg.a << 24);
int first_row = rowHeight * line + font->strikethrough_top_row + ystart;
TTF_drawLine_Blended(font, textbuf, first_row, SDL_min(line_width, textbuf->w), pixel | (Uint32)fg.a << 24);
}
}

Expand Down

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