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Remove an unused workaround and fix up the comments in the glyph cache

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This old workaround is not necessary and could not be used anyhow since
it would affect a way too wide range of drivers. Modern drivers should
be able to honor the default GL_UNPACK_ALIGNMENT of 4 even for 1 byte
per pixel formats like GL_ALPHA. Instead, document why the behavior
is correct.

Change-Id: I1687448ba92875c8ff772ccc371894e88ff64096
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>
This commit is contained in:
Laszlo Agocs 2014-05-12 18:11:25 +02:00 committed by The Qt Project
parent 12ba0d2cb3
commit 2406a8b45f
1 changed files with 2 additions and 29 deletions
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31
src/gui/opengl/qopengltextureglyphcache.cpp
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@ -408,41 +408,14 @@ void QOpenGLTextureGlyphCache::fillTexture(const Coord &c, glyph_t glyph, QFixed
#endif
funcs->glTexSubImage2D(GL_TEXTURE_2D, 0, c.x, c.y, maskWidth, maskHeight, fmt, GL_UNSIGNED_BYTE, mask.bits());
} else {
// glTexSubImage2D() might cause some garbage to appear in the texture if the mask width is
// not a multiple of four bytes. The bug appeared on a computer with 32-bit Windows Vista
// and nVidia GeForce 8500GT. GL_UNPACK_ALIGNMENT is set to four bytes, 'mask' has a
// multiple of four bytes per line, and most of the glyph shows up correctly in the
// texture, which makes me think that this is a driver bug.
// One workaround is to make sure the mask width is a multiple of four bytes, for instance
// by converting it to a format with four bytes per pixel. Another is to copy one line at a
// time.
#if 0
if (!ctx->d_func()->workaround_brokenAlphaTexSubImage_init) {
// don't know which driver versions exhibit this bug, so be conservative for now
const QByteArray versionString(reinterpret_cast<const char*>(glGetString(GL_VERSION)));
glctx->d_func()->workaround_brokenAlphaTexSubImage = versionString.indexOf("NVIDIA") >= 0;
glctx->d_func()->workaround_brokenAlphaTexSubImage_init = true;
}
#endif
#if 0
if (ctx->d_func()->workaround_brokenAlphaTexSubImage) {
for (int i = 0; i < maskHeight; ++i)
funcs->glTexSubImage2D(GL_TEXTURE_2D, 0, c.x, c.y + i, maskWidth, 1, GL_ALPHA, GL_UNSIGNED_BYTE, mask.scanLine(i));
} else {
#endif
// The scanlines in mask are 32-bit aligned, even for mono or 8-bit formats. This
// is good because it matches the default of 4 bytes for GL_UNPACK_ALIGNMENT.
#if !defined(QT_OPENGL_ES_2)
const GLenum format = isCoreProfile() ? GL_RED : GL_ALPHA;
#else
const GLenum format = GL_ALPHA;
#endif
funcs->glTexSubImage2D(GL_TEXTURE_2D, 0, c.x, c.y, maskWidth, maskHeight, format, GL_UNSIGNED_BYTE, mask.bits());
#if 0
}
#endif
}
}