This is related to one of my other questions.
If I am tiling a large image by creating a separate QGraphicsItem (with the raster data as its pixmap), how do I keep track of the QGraphicsItem's position within the scene? Obviously for raster data, it is important to keep all the tiles "touching" to make a continuous image and they also have to be in the right place so the image doesnt look jumbled.
Does each tile have to have positioning methods that move it in relation to it's neighbors on the top/left/bottom/right? This seems kind of clunky. Is there a better way to make them all move together?
In other words, if I pan the scene with scroll bars, or pick up the image and drag/move it around in the scene, I want all the tiles to also move and stay in the right position relative to each other.
What is the best approach for controlling the layout, which tiles need to be rendered (i.e. only the visible ones), and populating the data only once it is needed? Also, once a tile has been rendered, is the data from it ever dropped, and repopulated from the image file, say if it stays out of view for a while, then comes back later if someone pans to that section?
There are (more than) 2 ways of doing this:
Use QGraphicsItemGroup which
handles grouping of your tile items
for you. It moves, selects, updates
it's group members as if they are
one. I've never used it but from the
doc, it seems to work with typical
applications.
Paint the tiles yourself in the
paint() of one custom item. This
gives you total control on how to
place and draw the tiles while the
item truly acts as one item since it
is, well, one item. This is what I
do.
Related
I'm creating a simple chat client and server and I'm having some issues with how sf::Text is rendered. Say in the chat history for example. When users type their messages, the old messages will be pushed up. Eventually the message hits the top and I'll want to only display the part of the message that is still within the chat history. This is where I'm lost.
The element containing the text has two visible objects - sf::RectangleShape (the background for the text) and a sf::Text. I can easily adjust the size of the shape once it hits the top so it's not visible outside the chat history, but I can't adjust the size of the text without distorting the contents. Changing the character size obviously isn't ideal either.
What I want is to cut the text in half horizontally if half of the text is outside the chat history. My first thought was to mask it somehow but it seems like SFML has no support for that.
The reason I'm mentioning sf::Texture in the title as well is because I've had the same issue with that in the past. I just couldn't find a way to cut off parts of it, I only managed to distort it.
Is this possible at all in SFML?
One way of doing this is to draw the chat history to a sf::RenderTexture, which is the tool used for off-screen rendering.
Once you've drawn the chat history to your render texture, you can draw the texture on to the screen.
So if you place text that is half on the render texture and half outside, only the part that actually fits on there will be drawn.
Be aware though that render_texture are fairly expensive to construct, so you you want to re-use them and not create new ones all the time.
I'm building an application that plots measurement data using the QtCharts library. Some important things that should be mentioned are:
I am dealing with time series.
The measurement data is obtained offline, which means it has already been obtained. My program just reads it from the file and displays it.
I am working with a for-loop that takes the data points as chunks of a fixed size (say 10000) and adds them to the scatter series. This way, the data is being "replayed" and the user can see the progression of the measurement data at many intermediate time points and not just after all data points have been plotted.
I am working with a whole lot of data points, on the order of millions.
At every iteration of the loop a new QScatterSeries is created, data points are appended, the scatter series is added to the chart and then the chart view is repainted. In the beginning it is quite fast, but as time progresses the number of points to be painted increases and the painting process becomes slower and slower.
I know for a fact that I can reimplement the paintEvent of the chart view class to get it to redraw only part of itself. I think I can make it faster by updating only the parts that have new data points. I will just calculate the coordinates of the region where new data points were added and use the paintEvent. But how do I do it? I tried using the setClipRect() method of QPainter, but couldn't do it. Thanks in advance.
QGraphicsView/QGraphicsItem don't implement it.
They don't because it's unfortunately generally impossible: the displayed items (e.g. series) are scaled and antialiased. In the old days when everything was displayed in device units, and was drawn directly on the window, doing partial updates made sense: you'd first use a fast blit to shift the existing plot, and then draw new points.
Alas, in any non-trivial scene viewer, the relationship between the horizontal device (widget) units and the item (chart/series) units is not 1:1, so there's no general way to scroll the data in device units and have it still make sense in chart units.
There are is a workaround: Scroll by some larger-than-needed (rounded up) number of device units, then back-calculate what scroll it yields in chart units, and then offset the chart by such a number (i.e. move the X axis range accordingly).
This could be implemented with relative ease in the sources of the QGraphicsView system, as the chart builds on it. There's no way to "bolt this on" externally - you need to add such support directly to QGraphicsView and QGraphicsItem infrastructure, and then have the QChartView leverage it. If you're not in the habit of building your own Qt, you can of course copy the necessary classes over to your codebase and rename them.
I am wondering how can I add a border & background to labels generated via CCLabelBMFont class in cocos2d.
I don't want to use sprites because my labels are generated on the fly and will keep changing and the size of labels are also different.
Also, I want user to touch and move these labels across the screen. When user picks a label it wiggles a bit like in free air. In that case, I wish to keep low complexity and preserve memory and cpu calculations.
Anyone knows best ways to achieve this?
IOS app LetterPress has similar effects.
Create your own class, that will incapsulate creation of complex node.
It will have several layers, for example, the first layer can be simple CCLayerColor of given rect with zOrder -2, the next layer will be your CCLabelBMFont with zOrder -1 and then you can overload draw method to draw border over your control. All that you draw in this method will be drawn with zOrder 0.
Then you can encapsulate any effects in this class. For example, you can rotate it a bit with method pick, etc. Whatever you want.
Is there any way to change the touch priority for cocos2d iOS sprites? What I have are multiple cards on the screen and they are arrayed in an arc, just like it would when you hold them in your hands. So in this setup, they overlap, and I need to recognize on which card the touch was made. I could measure the coordinates of each vertex of cards and determine the visible area of a card and then check if the touch was made inside that area (couldn't I?) but I thought there would be an easier way to deal with this, say changing the touch priority? Which means that the card closest to the screen would have the highest priority and it'll keep decreasing along the way into the background, so that even if the touch was made on 2 sprites at once (the above and below one), it would be registered only on the sprite with higher priority.
Reading on the internet only revealed ways to change the priority for a sprite and layer so that it defines whether the touch was made on the layer or the sprite, but that's not what I want.
As far as I know, by default you get exactly that behavior, the sprites closer (on the z ax) to you have priority. However, I think they pass down the event to the ones behind them as well. So, what i think you need to do is to eat the event when it gets to any of your sprites. To do that, just return NO when overwriting the "touchBegin" method. Hope it helps.
I have a ListView-like control that displays a list of items of various heights. The contents of the list, and the heights of the items can change – a background thread is populating the list and calculating the layout of each item, possibly even while the user is scrolling the content.
Which brings me to my question: How do I display a useful vertical scrollbar for this view? I’ve seen cases (notably web browsers) where the slider “jumps away” from the mouse cursor while the user is dragging it, the result of the underlying content growing in height. I don’t want that.
So far
Instead of the slider representing the viewport height relative to the content height, maybe it could represent a point in a timeline instead? (The items are sorted by timestamp). This would at least prevent the scrollbar from changing as item layouts are calculated.
Get rid of the scrollbar altogether and use a forward/backward rocker switch like the one used in Picasa (the further the slider is pulled upwards or downwards, the faster the view is scrolled, until the user releases the slider). If I take this route, are there any controls you can recommend?
I am using Qt, but this applies to UI design in general.
IMO the fundamental problem with a classic scrollbar is that due to background population, the valid range is changing - and thus, the meaning of a scrollbar position changes.
If you can predict the full range of items, you can still provide a scrollbar and replace yet-unknown items with "loading...".
Otherwise, a rocker (is that an official name?) would be the next best thing to use.
However, since you have a dedicated scale (timeline), it might be better to have separate buttons that jump a dedicated time (e.g. one minute, one hour, one day, ..). For a fancier look, you could create a rocker with "hot" areas that jump for a specific time, whereas the areas inbetween are interpolated (linear or or logarithmic, depending on the scale to cover).
i.e. line this (drawing just the "backward" half):
--------------------------
|##|XXXXXXX|##|XXXXXXX|##|
--------------------------
-1h -1m -1s