I'm developping an editor that must use SVG shapes to create diagrams.
To open and display SVGs I use librsvg which is actually pretty good but only useful to render SVGs not to edit them.
I would like to access to shape's property and change their values (i.e. width, size ).
I use Cairo to draw them to the screen but I don't want to use the cairo's scale feature, cause it's not the same as changing the size of the shapes.
I use C++ builder XE3 on Win32.
Is anyone knows a good C/C++ library I could use to do so ?
Thanks for your help.
Cairo's scale function scales the entire coordinate system, but you can use it on an individual shape if you translate first to the shape's origin; and if you bracket these changes with a save/restore pair it will only affect drawing done within this span. Resetting the matrix before stroking allows you to resize a drawing without changing the stroke-width (alternately, you can adjust the stroke_width by 1/scaling-factor).
cairo_matrix_t m;
cairo_get_matrix(cr, &m);
cairo_save(cr);
cairo_translate(shape_x, shape_y);
cairo_scale(shape_w, shape_h);
//cairo_move_to(cr, x, y); //perform the actual drawing
//cairo_line_to(cr, x, y);
//cairo_closepath(cr);
cairo_set_matrix(cr, &m);
cairo_stroke(cr);
cairo_restore(cr);
And if resetting the matrix explicitly like this, you don't actually need the save/restore anymore (translate and scale don't affect anything but the matrix, and stroke resets the path).
Related
I'm using the Qt C++ ArcGIS Runtime SDK v100.9 and I have various shapes and labels being drawn on a map.
I want to be able to find out the area (bounding rectangle) of Graphic (which is a text label (TextSymbol) at a given point (SpatialReference::wgs84) on the map) so I can determine if the width of the label is more or less than another Graphic (lets say it has a Polygon for its Geometry which is being used to draw a circle) in order to decide if the label should be set to visible or not.
Within a class derived from Esri::ArcGISRuntime::MapGraphicsView the circle and the text label are created along the lines of:
Point centerWgs84(0.0, 0.0, SpatialReference::wgs84());
Graphic* circleGraphic_p = new Graphic(GeometryEngine::bufferGeodetic(centerWgs84, 1000.0, LinearUnit::meters(), 0.5, GeodeticCurveType::Geodesic));
this->graphicsOverlays()->at(0)->graphics()->append(circleGraphic_p);
circleGraphic_p->setSymbol(new SimpleLineSymbol(SimpleLineSymbolStyle::Solid, QColor(Qt::blue), 1.0));
circleGraphic_p->setVisible(true);
TextSymbol* textMarker_p = new TextSymbol("Some Label", Qt::black, 12.0, HorizontalAlignment::Center, VerticalAlignment::Bottom);
Graphic* labelGraphic_p = new Graphic(centerWgs84, textMarker_p);
this->graphicsOverlays()->at(0)->graphics()->append(labelGraphic_p);
labelGraphic_p->setVisible(true);
Rather than always setting the label visibility to true, I thought I would be able to take the Geometry of each Graphic and use it to construct an Envelope which would allow me to then get the width of each envelope that could then be compared:
Envelope circleEnvelope(circleGraphic_p->geometry());
Envelope labelEnvelope(labelGraphic_p->geometry());
labelGraphic_p->setVisible(circleEnvelope.width() >= labelEnvelope.width());
but when I try and do this, the width of each envelope is always a very small negative value (such as -2.25017... e-98)
Any suggestions on what I am doing wrong or if there is a better way to get the size on the map (or in device independent units) of the text label and a Graphic described by the Geometry of a Polyline or Polygon?
EDIT: I've discovered that the Geometry object has an extent() method from which I can get the width of the circle but the Geometry of the Graphic being used for the text label results in a width of zero from its extent() method. I expect this is because the Geometry is just a Point which has no width or height. So the question still stands of how to get the bounding rectangle of a TextSymbol?
You are correct, the extent is being returned of the underlying geometry, not the TextSymbol. I don't think you will be able to achieve what you are wanting in the way you are going about it, as there isn't a way to get the bounding box or screen coordinates of the symbol itself. Instead, have you considered using LabelDefinitions and setting the various deconfliction options? This sample shows labels on layers, but can be applied to graphics as well. There are many labeling options you can apply, and this would allow the internal labeling engine to deconflict for you.
I am trying to rotate am image around its origin(center) in QT using QWidgts in C++. I experimented a lot of things here, but no matter what I do, the image keeps rotating around some arbitrary position I have no clue of. Kindly, help me out here. I am new to QT.
void gaugeWithRedZoneImage::rotate()
{
QPixmap pixmap(*gaugeMainScreen->pixmap());
QMatrix rm;
rm.translate(0, 0);
rm.rotate(-360);
pixmap = pixmap.transformed(rm);
gaugeMainScreen->setPixmap(pixmap);
/*QTransform rotate_disc;
rotate_disc.translate(pixmap.width()/2.0 , pixmap.height()/2.0);
rotate_disc.rotate(-60);
rotate_disc.translate(-(pixmap.width()/2.0) , -(pixmap.height()/2.0));
pixmap = pixmap.transformed(rotate_disc);
gaugeMainScreen->setPixmap(pixmap);*/
}
Form the documentation of QPixmap::transformed():
The transformation transform is internally adjusted to compensate for unwanted translation; i.e. the pixmap produced is the smallest pixmap that contains all the transformed points of the original pixmap.
This means that the method ensures no clipping takes place by appending the canvas. No matter what your rotation center was, the automatic extension of canvas will almost always result in a perceived shift.
Image examples might help to further diagnose the problem.
As ypnos said, your problem isn't the rotation center. When you rotate your image, its width and height will most likely change and no longer fit your container (gaugeMainScreen) dimensions.
You have some possibilities to overcome this problem. One of them is to set your container to scale its contents (you can use the method setScaledContents()). In this case, you have to keep the original image around and use it whenever you apply a rotation, otherwise your image will appear increasingly smaller.
I have started to create a paint program that interacts with drawing tablets. Depending on the pressure of the pen on the tablet I change the alpha value of the line being drawn. That mechanism works.
Thin lines look decent and it looks a real sketch. But since I am drawing lines between two points (like in the Qt scribble tutorial) to paint there is an alpha overlap between the line joints and it is very noticeable for thick strokes.
This is the effect with line to line conjuction:
As you can see, there is an ugly alpha blend between the line segments.
In order to solve this I decided to use a QPainterPath to render lines.
Two problems with this:
A long, continuous, thick path quickly lags the program.
Since the path is connected it acts as one, so any change to the alpha value affects the the entire path(which I don't want since I want to preserve a blending effect).
The following images use a QPainterPath.
The blend effect I want to keep.
The following image shows the 2nd problem which changes the alpha and thickness of the entire path
The red text should read: "if more pressure is added without removing the pen from the tablet surface the line thickens" (and alpha becomes opaque)
Another thing is that with this approach I can only get a blending trail from a dark to light (or thick to thin path width) but not light to dark. I am not sure why this effect occurs but my best guess is that it has to do with the line segments of the path updating as whole.
I did make the program increase/decrease alpha and line thickness based on the pressure of the pen on the tablet.
The problem is that I want to render lines without the alpha overlap and QPainterPath updates the entire path's alpha and thickness which I don't want.
This is the code that creates the path:
switch(event->type()){
case QEvent::TabletPress:
if(!onTablet){
onTablet = true;
//empty for new segment
freePainterPath();
path = new QPainterPath(event->pos());
} break;
case QEvent::TabletRelease:
if(onTablet)
onTablet = false;
break;
case QEvent::TabletMove:
if(path != NULL)
path->lineTo(event->pos());
if(onTablet){
//checks for pressure of pen on tablet to change alpha/line thickness
brushEffect(event);
QPainter painter(&pixmap);
//renders the path
paintPixmap(painter, event);
} break;
default:;
}
update();
The desired effect that I want as a single path (image created with Krita paint program):
To emulate the Krita paint program:
Keep a backup of the original target surface.
Paint with your brush onto a scratch surface that starts out completely transparent.
On that surface, your composting rule is "take maximum opacity".
Keep track of the dirty regions of that surface, and do a traditional composite of (scratch surface) onto (original target surface) and display the result. Make sure this operation doesn't damage the original target surface.
Now, you don't have to keep the entire original target surface -- just the parts you have drawn on with this tool. (A good tile based lazy-write imaging system will make this easy).
Depending on the segment size you are drawing with, you may want to interpolate between segments to make the strength of the brush be a bit less sharp. The shape of your brush may also need work. But these are independent of the transparency problem.
As for the Qt strangeness, I don't know enough Qt to tell you how to deal with the quirks of Qt's brush code. But the above "key-mask" strategy should solve your alpha overlap problem.
I do not know how to do this in Qt. Glancing at the Qt compositing modes I don't see an obvious way to say "take maximum" as the resulting alpha. Maybe something involving both color and alpha channels in some clever way.
I know this question is very old, and has an accepted answer, but in case someone else needs the answer, here it is:
You need to set the composition mode of painter to source. It draws both source and destination right now.
painter.setCompositionMode(QPainter::CompositionMode_Source);
If you want your transparent areas to show through underlying drawings, you need to set the composition mode of your result back to CompositionMode_SourceOver and draw over destination.
I don't know if you still look for an answer, but I hope this helps someone.
I am using QT and try to plot a graph with QGraphicsView and QGraphicsScene..i dont want any additional dependencies, thats why i dont use QWT. When i plot my data, at the moment i use
scene->drawLine(x1,y1,x2,y2,pen);
then this draws a line between the 2 points in the QGraphicScene. But this uses a top left x=0 y=0 system... i would like to use my own system like in the picture below. Another problem is that i have double values from -3 to +3..has anyone some experience with QGraphicScene and QGraphicsView and can tell me how i can accomplish this?
Try looking into QGraphicsView::setTransform. This matrix defines how "scene coordinates" are translated to "view coordinates", it's a common concept in graphics programming.
There are also convenience functions scale(), rotate(), translate() and shear() which modify the view's current transformation matrix.
So you could do something like this:
scale(1.0, -1.0); // invert Y axis
// translate to account for fact that Y coordinates start at -3
translate(0.0, 3.0);
// scale Y coordinates to height of widget
scale(1.0, (qreal)viewport()->size().height()/6.0);
And since this is dependent on the size of the widget, you'd also want to catch any resize events and reset the transformation matrix again there. Assuming you want "3" to represent the top of the viewport and "-3" the bottom.
Hi i want to develop game like 'Doodle jump'.But i have some problem with the following features-
1.How to move background scene/image.
2.How to detect collision between object.Is it needed a physics engine like box2d or i should just use manual collision.
3.what should be the size of the background image.
4.In fact i have no idea how does background move .So i need a explanation from someone.
Background Movement
A) You could create a TMX Tilemap and then make a very high Tiled-Map.
B) You could create one texture and then cycle the texture coords instead of really moving it.
Detect it manually. Best is detect it via "Point in Boundingbox" or "Rect in Rect".
For more detail visit my blog entry for collision detection with cocos2d : http://www.anima-entertainment.de/?p=262
Size of an Image
Keep in Mind that textures are always at power of 2 in the memory. If you want to create one Background-Image at retina highresolution (960x640 Pixel) in the memory will be a texture of 1024x1024. If possible use smaller Background-Images and stretch them. (like 512x512). But I really would recommend for big scrolling images the TMX Support.
CCTMXTiledMap * tmxNode = [CCTMXTiledMap tiledMapWithGMXFile:#"Level.tmx"];
// lets say you want to move it 50 pixels down in 1 second :
[tmxNode runAction:[CCMoveBy actionWithDuration:1.0 position:ccp(0,-50)];
To create a tilemap : http://www.mapeditor.org/
In the folder of cocos2d, you could get many demos of tilemap.
TileMapTest.h
TileMapTest.m
refer this tutorial this will helpful for you.
http://www.raywenderlich.com/2343/how-to-drag-and-drop-sprites-with-cocos2d
this is used screen movement with pan recognizer