Optimized glyph uploads in GL texture cache.

Avoid doing a lot of glTexSubImage2D calls in favor of doing a single
call (even if it involves an additional image copy).

Reviewed-by: Eskil

3 files changed, 19 insertions, 2 deletions

diff --git a/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp b/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp
index 4362c0a..9e8e828 100644
--- a/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp
+++ b/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp
@@ -339,8 +339,19 @@ void QGLTextureGlyphCache::fillTexture(const Coord &c, glyph_t glyph, QFixed sub
         // by converting it to a format with four bytes per pixel. Another is to copy one line at a
         // time.
 
-        for (int i = 0; i < maskHeight; ++i)
-            glTexSubImage2D(GL_TEXTURE_2D, 0, c.x, c.y + i, maskWidth, 1, GL_ALPHA, GL_UNSIGNED_BYTE, mask.scanLine(i));
+        if (!ctx->d_ptr->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)));
+            ctx->d_ptr->workaround_brokenAlphaTexSubImage = versionString.indexOf("NVIDIA") >= 0;
+            ctx->d_ptr->workaround_brokenAlphaTexSubImage_init = true;
+        }
+
+        if (ctx->d_ptr->workaround_brokenAlphaTexSubImage) {
+            for (int i = 0; i < maskHeight; ++i)
+                glTexSubImage2D(GL_TEXTURE_2D, 0, c.x, c.y + i, maskWidth, 1, GL_ALPHA, GL_UNSIGNED_BYTE, mask.scanLine(i));
+        } else {
+            glTexSubImage2D(GL_TEXTURE_2D, 0, c.x, c.y, maskWidth, maskHeight, GL_ALPHA, GL_UNSIGNED_BYTE, mask.bits());
+        }
     }
 }
 
diff --git a/src/opengl/qgl.cpp b/src/opengl/qgl.cpp
index 76621e9..bff38d7 100644
--- a/src/opengl/qgl.cpp
+++ b/src/opengl/qgl.cpp
@@ -1735,6 +1735,9 @@ void QGLContextPrivate::init(QPaintDevice *dev, const QGLFormat &format)
     workaround_brokenTextureFromPixmap = false;
     workaround_brokenTextureFromPixmap_init = false;
 
+    workaround_brokenAlphaTexSubImage = false;
+    workaround_brokenAlphaTexSubImage_init = false;
+
     for (int i = 0; i < QT_GL_VERTEX_ARRAY_TRACKED_COUNT; ++i)
         vertexAttributeArraysEnabledState[i] = false;
 }
diff --git a/src/opengl/qgl_p.h b/src/opengl/qgl_p.h
index 5508598..5a5e5cc 100644
--- a/src/opengl/qgl_p.h
+++ b/src/opengl/qgl_p.h
@@ -416,6 +416,9 @@ public:
     uint workaround_brokenTextureFromPixmap : 1;
     uint workaround_brokenTextureFromPixmap_init : 1;
 
+    uint workaround_brokenAlphaTexSubImage : 1;
+    uint workaround_brokenAlphaTexSubImage_init : 1;
+
 #ifndef QT_NO_EGL
     uint ownsEglContext : 1;
 #endif