I have two FBOs created using QOpenGLFrameBufferObject, which are images with a transparent background and some lines and text on top of them. I am blitting the first fbo onto the second using QOpenGLFramebufferObject::blitFramebuffer, this results in the content of the first fbo on top of the second. However, I would like to preserve the transparency of the the first fbo and blend the content of the first fbo on top of the second fbo (instead of erasing the portion of the second fbo and redrawing the first fbo on top of it). Looking around, I think this might be possible with glBlendFunc, but the following didn't really achieve the result I wanted.
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
// then blit fbo1 on top of fbo2
QOpenGLFramebufferObject::blitFramebuffer(fbo2, fbo1);
How can I preserve the transparency (by blending them together) of my framebuffers when I blit them?
You can't glBlitFramebuffer is a copy operation, and does not blend the source and target fragments.
A possibility is to render to a texture (see Framebuffer Object - Attaching Images). Finally you can render a screen space rectangle and Blend the texture with the target framebuffer.
Related
I'm using Qt3D with a combination of this offscreen renderer and modified the framegraph to include a background image, like here.
Unfortunately, adding transparency to the objects drawn over the background image using QPhongAlphaMaterial only works unsatisfactorily.
This is th result:
What you can't see here is that the whole circle part is actually transparent, i.e. the renderer wrote the transparency value of the object for the whole pixel instead of adding it transparently on top of the background.
This is what the rendered object looks like wihtout transparency:
And this is the background:
The framegraph has two branches: one for the backgroun image, which is processed first, and one for the objects. I added a QRenderStateSet for the objects that contains a QBlendEquation with the blend function set to add and a QBlendEquationArguments with source RGB and alpha set to 1, and destination RGB and alpha set to 1 minus source alpha.
Any ideas how to fix this problem?
(For anyone wondering, I took the images from the T-Less dataset and wrote a program to create ground-truth data for 6D pose estimation)
Similarly to this question, the format of the texture that is being rendered to needs to be set to RGB8_UNorm and not RGBA8_UNorm, i.e. without the alpha channel.
I have a transparent QGraphicsWebview inside a QGraphicsView with the following settings:
The QGraphicsView is the high level widget, and is shown in full screen mode
The graphics view uses a QGLWidget as its view port (to use opengl-es)
Alpha channel and double buffering are enabled in this QGLWidget
Transparency is achieved by graphicsView->setStyleSheet("background:transparent")
Following attributes are set for QGraphicsView and QGraphicsWebview
WA_TranslucentBackground = true
WA_NoSystemBackground = true
WA_OpaquePaintEvent = false
The QPalette::Base and QPalette::Window brushes of webview and webview->page() are set to Qt::transparent
At the beginning, the transparency works fine. But as the screen get updated (when I scroll), it looks like the new bitmap is blended on top of the existing one to get a superimposed picture. After about 5-6 screen updates, this blending causes the colors to accumulate and form an opaque rectangle (with a corrupted image). Following images show first, second and final stages of the problem.
How do I tell qt/opengl to stop blending and just draw the new image to the frame buffer?
I tried calling fillRect(boundRect(), Qt::transparent) from overridden Webview::paint and GraphicsView::paintEvent; but it didn't work except for making the updates slower.
I am new to Qt and OpenGl, so I might be missing some basic flags or settings.
I tried all the methods mentioned above. They did not work for me. I then debugged into qtbase code and found that setting the Opacity level make the top browser layer transparent.
this->setOpacity(0.1);
this pointer points to the QGraphicsWebView object.
With this method, the whole front browser contents including background will be transparent. To separate header, paragraph and background and to specify different transparent levels for them, I will have to dig into webkit code a little further to figure out the problem. But for now, setOpacity() did the trick and is good enough for what I am doing.
It turns out the problem is graphicsView->setStyleSheet("background:transparent");. Who would have guessed?!
Yeah, the line that I thought made transparency work was actually causing troubles with transparency. The application works fine without that line (or if you change it to background:none)
In short, steps to get a transparent QGraphicsWebview using QGLWidget:
Set the Base palettes of QGraphicsWebview, QWebpage and the outer QGraphicsView to Qt::transparent
scene->setBackgroundBrush(QBrush(Qt::transparent));
You should also make sure that html body background is set to transparent values:
html, body {
background-color: rgba(127, 127, 0, 0.5);
}
I am creating a circuit schematic editor using Qt Creator. I have a QGraphicsScene/QGraphicsView canvas that I would like to drop images of circuit components onto and move them around.
I am currently using a pixmap QGraphicsItem and adding it to the canvas and making it movable. This works great when you click directly on the symbol's lines, however the symbol does not move when the transparent areas in the image are clicked.
Is there a way to expand the hitbox/mouse area to make these transparent regions respond the same as the other regions do on the symbol? Below is how I am adding the image. (I need the image transparent so that other symbols are visible behind/infront of it)
QGraphicsItem* b = canvas.addPixmap(QPixmap(":/images/ground2.gif"));
b->setFlag(QGraphicsItem::ItemIsMovable);
b->setPos(qrand()%int(canvas.width()),qrand()%int(canvas.height()));
All help is much appreciated! Thanks!
Josh
You can call QGraphicsPixmapItem::setShapeMode( QGraphicsPixmapItem::BoundingRectShape ) to have the item treated a rectangle.
I have a full size QGLWidget which paints the application background using QPainter (might change to native openGL commands in the future).
On top of this QGLWidget I use QWidgets (non-GL) for the user interface elements. These are, for example, QLineEdits and QPushButtons. I put them into a custom painted QWidget which uses semi-transparent background painting. The paintEvents of the QLineEdit and QPushButton are overwritten and use semi-transparent backgrounds, too.
The whole UI should look like the following (This is a screenshot where I disabled OpenGL and used QWidget instead of QGLWidget for the background. Note the semi-transparent top bar which also draws a shadow (within its own region)):
When the QLineEdit has the focus, it should have a higher opacity but still not fully opaque:
So now, with OpenGL enabled (The background then is a QGLWidget), the semi-transparent widgets above don't paint on top of the background but on (it seems to be) uninitialized data. The image shining through the top bar is sometimes the whole window itself and sometimes other windows currently being on my desktop.
This currently looks like the following (In this screenshot, the data on which the semi-transparent painting operations are painted on seems to be an image of the widget itself, having an offset.):
When I wrote text into the line edit (here: "This is some text which has been there before!"), removed it and set the focus back to the background widget (so the magnifier icon and the placeholder text appear), the previously painted things still shine through (Note that the visible border should not be visible anymore, but also still shines through):
So the problem is: Instead of being painted on top of the underlying widgets, the semi-transparent widget is painted on top of the old results, initially being something like "uninitialized memory".
Why does this happen? How can I solve the problem?
Things you should know before answering:
The background scene is a composition of tiles which are rendered off-screen. So it can be painted very fast and repainting of the background for every little change of the overlay isn't problematic.
The top bar is a custom QWidget with manual painting and arrangement of the contained two widgets (the button and line edit).
The two widgets overwrite the paintEvent, only draw their own (semi-transparent) background when they have focus and don't use frames already provided by Qt. So the white border in the second screenshot is drawn in my custom paintEvent.
I want the background and the composition of overlay widgets to be separately implementable. The background is an AbstractMapView which has some concrete map view classes. The whole window is an AbstractView (there are multiple concrete views, too), which contains both a concrete map view and the overlay widgets, composed in a way itself decides. Therefore, I don't want the logic of the overlay widgets to be part of the underlying map view. (I hope you understood this, as it is a bit complicated.)
This sounds like an issue where the GL content (i.e. your background aka the QGLWidget) is not in the Qt context. While I'm not a pro on GL painting with Qt, you may want to look at this discussion regarding GL painting and a QLabel for some direction/potential hints.
http://www.qtcentre.org/threads/40335-QLabel-on-top-of-a-QGLWidget-background-issue
In short, we here at the office use OpenGL painting and offscreen rendering of maps and it's very important to make sure Qt is aware of the pixels so your foreground widgets can have the semi-transparency applied to their backgrounds.
The particular product we use also renders the map in tiles and supports providing the GL output in a buffer (i.e. it's call a snapshot and is provided as a bitmap) at which point we use the paintEvent of a regular QWidget to paint the buffer so that the painted pixels are in Qt context.
You can define a Qframe with Qt::SplashScreen flag as the search box and set its opacity. Put your widgets inside it such as the search textbox and positon it where it should appear on the mainwindow. It will also be a good idea to reposition it as the mainwindow is moved or resized overriding its moveEvent.
I am using bitmapData and bitmap classes to render a mouse cursor on the display screen. The bitmapData consists of an area whose colors should be inverted according to the background color. This is a very basic thing which could be observed with text cursor(the vertical line with two small horizontals on top and bottom), when moved over the text area.
I want to be able to do the same with the pixels in my bitmapData, is there a way to find out the background color effectively and invert the color values?
In this process i will be redrawing the whole pixels, is there any other efficient way to do that ?
You can draw your cursor using BlendMode.INVERT
http://livedocs.adobe.com/flex/3/langref/flash/display/BitmapData.html#draw()
or simply put your cursor display object over your bitmap and set it's blendMode to INVERT.