Here is the thing, I have develop a manual Annotation Tool for annotating images, you know, use rectangles to mark parts of a human, head, torso, limbs, and store the information like width, height, center point, rotation. I use QT to develop this tiny tool, it's cool, but I face a problem. I want to save the pixels of the image which in a QGraphicsScene in the area of the rectangles (QGraphicsItems), so, I want to know how can I control the pixels of this area?
Thank you very much.
You can render the rectangle area into a QPainter which can be a QImage:
http://qt-project.org/doc/qt-4.8/qgraphicsscene.html#render
Related
I created a QQuickItem which can display a lineplot. This has been done using QSGNodes and should thus be hardware accelerated via OpenGL (as I need to plot many points). Now I want to add an axes to this this plot, and for this I need to draw some lines for the Axis, Ticks (and maybe include a svg for the Arrow head on the axis) and have some text labels.
Does it hurt performance, if I implement this axis as a QQuickPaintedItem or using the Canvas? I am not worried about the performance of drawing the axis, but would my lineplot QQuickItem still be using OpenGL if there is a QQuickPaintedItem at the same place?
Note that SVG files are rasterized and drawn as raster bitmaps, they are not drawn using geometry, so having a SVG won't really save you much aside from the space the image takes on disk, as far as the GPU rendering is concerned, it is just a bitmap. If you want to draw it using geometry, go for QQuickItem and QSGNodes combo again.
QQuickPaintedItem or Canvas- both work in the same way, only the drawing for Canvas is done from JS, so it will be a tad slower. However, it may be a non issue as you typically don't have to redraw chart axis that much.
Of course, each element will be rendered with its respective backend, no need for concern there.
Here's the issue at hand. I need to be able to pick a background (an image showing an object, let's say, a starship model). I want to be able to apply various previously prepared textures to various areas on it, as some kind of a "colour your own object" app, but without the need to prepare dozens of individual segments.
Ok, so this is one, newbie way to do it. We have those images:
Two kind of different versions, an original photo and a quickly Photoshopped one. Let's say we only want the Borg-ish green deflector and warp nacelle from the second picture, without the odd pink hull. You have to have a mask, basicly an image of an equal resolution (or at least the same aspect ratio, which you can reliably scale to image's resolution), with the area filled with color (or whatever else), and transparent area everywhere else. As the mask, I've used a few strokes of brush on an empty layer, set to overlay mode, and then saved as PNG, with transparency. And this is how the code went:
First, import images.
QPixmap background("orig.png"); //import base image
//import alt version/texture/whatever you want, anything will work with a good mask
QPixmap element("alt.png");
QPixmap mask("deflector.png"); //mask. Just nacelles and deflector.
Then, isolate the area that interests us from alt version
QPainter painter(&element);
painter.setCompositionMode(QPainter::CompositionMode_DestinationIn);
painter.drawPixmap(0, 0, mask.width(), mask.height(), mask);
And finally draw it onto the target object.
QPainter inter(&background);
inter.drawPixmap(0, 0, element);
ui->label->setPixmap(background);
The result:
This method respects any and all transparency you could've done in Photoshop or another image editing software.
Simple, but an effective solution, for when your app has to work with graphics prepared by someone else, elsewhere.
I have an SCNNode that has its geometry populated from a collada file (.dae) and displays correctly on screen. I can apply materials to the geometry easily enough, however I'd like to change the scale of the material.
I currently populate it with
nodeArray[0].geometry?.firstMaterial!.diffuse.contents="wood.png"
but the scale of the material is too small. While I can edit the png in GIMP or something similar and import it as wood2.png is there any way I can set the material scale programatically?
what do you mean by "too small" ?
Geometries are made of different sources such as the vertices' positions, but also their texture coordinates. These texture coordinates (they belong in [0,1]x[0,1]) are specified per vertex and indicate where to look in the texture.
In your 3D modeler please check that your texture coordinates match what you want (i.e. they cover the whole image i.e. they go from 0 to 1 in very direction), and make sure that your image has no extra transparent margin or other wasted space.
You can have a look at SCNMaterialProperty's contentsTransform property. But please check your model and texture before using it.
You need to open your UV snapshot in an image editing software like Photoshop, scale the wood texture in Photoshop over your UV's, then resave your PNG/JPG, move PNG/JPG back to Xcode
I am making an app using Qt (currently 4.8) which displays a literal map from a large number of QGraphicsScene items. I would like to annotate the view with a scale. My requirement for the scale is that it is permanently fixed w.r.t the viewport widget. It needs to be updated whenever the view scale changes (zoom in, etc). There are other possible overlay items as well (compass, etc) so I'd prefer a generic solution.
I have looked at earlier questions around this which suggest:
using the ItemIgnoresTransform
using an overlay pixmap.
I tried IgnoresTransform but that way didn't work right: I couldn't figure out how to fix it in place in (say) the bottom corner of the viewport and was having some difficulty getting the text and lines always displaying in the correct size.
I scrapped that and subclassed QGraphicsView, adding an overlay pixmap by reimplementing the paintEvent (calls original one, then paints the overlay pixmap on top), and an alignment option to indicate where it goes. Coding some pixmap paint code produces a usable scale on the view. Yay! ... but it doesn't work with scrolls - I get "shattered" renderings of the scale all over, or sometimes no scale at all. I think this is because QGraphicsView::scrollViewportBy() uses viewport()->scroll() so I wondered if switching to ViewportSmartUpdate would help, but it doesn't help enough. I'd prefer not to switch to ViewportFullUpdate as that would likely slow the app down too much (there are millions of items in the scene and that would require a full repaint just to move around).
So. Any ideas from here? Would adapting my pixmap code to write to a new mostly-transparent Widget that is overlaid on the viewport be a better way?
Thanks for any help...
Though it may not be the best way of doing this, in the past I've added custom widgets to the window that holds the QGraphicsView / QGraphicsScene, which have the same graphic style as the QGraphicObjects in the scene. When the view is then used to move objects in the scene, or the scene itself, the items on the window remain in the same place.
Hope that helps.
I want to develop an image editing application in Flex 4. My initial requirement is to draw various shapes like Line, Rectablge, Triangle, Circle, Star etc in appication. I want to facilitate user to draw shapes using rubber banding like professional applications do.
All shapes would be vector and should look smooth in an size. So, can't use bitmap and scale them.
What are better methods to achieve this?
if you don't want to start from scratch with the basic shapes, there is this framework called degrafa: http://www.degrafa.org/
they have plenty of parametric shapes & curves and advanced features to organize them together.
Make shape editor with some control points. Control points are draggable sprites (circles or squares as you like). When control point is moved, editor must be updated - it may be resize or move action. On resize, draw your vector shape according to new size. The easiest way to make sprite draggable is startDrag() function - you can also set limits there (to stay in editor area or to disable negative sizes).
I have done such editors based on Sprites, added into Flex application with rawChildren.addChild, but you can try to use Canvases instead of Sprites if you wish.