I was under the impression that if you do this in your application
QGuiApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
QApplication* app = new QApplication(temp, NULL);
then Fonts gets automatically scaled up on high resolution display. Same if you explicitly increase font scaling in Windows 10 (Settings-->System->Custom Scaling).
However, when running the following code with 100% and then 200% scaling in Windows 10, it does not return doubled size.
QFont font = QFont("arial", 10);
QFontMetrics fm(font);
int width = fm.width("abcdefgABCDEFG");
Strangely there is only 1 pixel difference.
100% --> width = 108 pixels
200% --> width = 109 pixels
Why is that? Can I get QFontMetrics to account for Windows scaling? Or do I need to use Logical / Physical DPI to deduce that font size must be increased by a factor 2?
Thanks
For the proper scaling of custom-drawn items use QScreen::physicalDotPerInch property to realize the scaling coefficient to apply to actual drawings:
qreal myScale = pScreen->physicalDotPerInch() / constStandardPerInch;
P.S. The question still needs to be revised.
Related
I have a Qt application and I need to adapt the application (zoom-in/zoom-out) as the scaling changes from the OS in Display Settings.
I have read from Internet that:
The standard DPI settings are 100% (96 DPI), 125% (120 DPI), and 150%
(144 DPI)
But, I am getting below DPI values when logged from the Qt application:
Scale - Physical DPI X - Physical DPI Y
100% - 158, 159
125% - 158, 159
150% - 79, 79
175% - 79, 79
So, as per the above values, the application text size has no difference for the 100% and 125% scale. Same behavior applies for 150% and 175%.
Below is the Qt code that I used:
#include <QWidget>
QApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
QWidget widget;
qInfo() << "Hello Qt";
int dpiX = widget.physicalDpiX();
int dpiY = widget.physicalDpiY();
qInfo() << dpiX;
qInfo() << dpiY;
Can anyone please guide? What I am trying to achieve is that the Qt application behaves (changes application size/ font size) depending on scaling set in Display Settings of the OS.
I initially suggested using QWindow::devicePixelRatio() in this answer. However, as of Qt 5.12, this does not actually work correctly yet. Qt will avoid fractional scaling ratios due to a bug in Qt's UI scaling implementation. So for 125%, it will still return a 1.0 scaling factor. At 175%, it will return 2.0 instead of 1.75.
So for now, you should fall back to querying the DPI. However, query the logical DPI, not the physical DPI as you are doing now. Replace calls to physicalDpi() functions with calls to logicalDpi() ones. This should give you the standard 96/120/144 DPI reported by Microsoft Windows.
The previous part of the answer below can be used once Qt fixes the bug.
Previous answer, applicable once Qt fixes their scaling bug
Query the scaling ratio directly, don't try to infer it from the DPI. You use QWindow::devicePixelRatio() for this. At 100% scaling, this will return 1.0. At 125% scaling, it will return 1.25. And so on. Since this is a scaling factor, you use it as a multiplier for your sizes.
You should call devicePixelRatio() on the window your widget is currently in. This is because different windows can be on different displays on multi-monitor setups.
The window the widget is in can be obtained with QWidget::windowHandle(). This can return null if the widget is not a window. So you should probably write a small helper function that returns the correct DPR (Device Pixel Ratio) for a widget. It should take a QWidget as argument, and if windowHandle() returns null for the widget, walk up the parent tree, calling windowHandle() on each parent until it finds the first one that doesn't return null. Then return windowHandle()->devicePixelRatio(). This will be the correct DPR to use in that widget.
I've enabled HDPI by setting QT_SCALE_FACTOR environment variable.
Then I've found that my main window appears somewhere behind the screen.
After some debugging I've found that frameGeometry() returns less than zero.
P.s. : There are 2 monitors in the system also. One has 96 dpi, other is in 144 dpi mode.
For example:
left top = {-1920, -30}
width, height = {968, 820}
Has anyone faced any similar problem?
I'm developing a psychology experiment in the browser. In order to keep the same viewing angle across people, I want to display two characters around 5 inches apart on the screen.
Is there any way to detect the real size of the monitor being used, and using the screen resolution and DPI, render the two objects the same real width apart? (I will only allow people that have real computers, e.g. not mobile)
I heard detecting real size may not be possible, if true, and assuming people will report to me the real size of their monitor, is this possible?
I'm using HTML5 Canvas, fwiw. Perhaps resizing this canvas w.r.t to the resolution and DPI is a solution.
No, unfortunately. The browser will always report 96 DPI. Without actual DPI you cannot produce exact measures in other units than pixels.
Even if you could the browser would only reflect the system DPI which in itself is just an approximation.
You need to "calibrate" for the individual device providing a mechanism to do so, e.g. a scale that can be varied and measure on screen. When it measures 1 inch you know how many pixels covers that inch, and then this value can be used as a scale for the rest.
Example on how to get screen DPI via "calibration"
var ctx = document.querySelector("canvas").getContext("2d"),
rng = document.querySelector("input");
ctx.translate(0.5, 0.5);
ctx.font = "16px sans-serif";
ctx.fillStyle = "#c00";
render(+rng.value);
rng.onchange = rng.oninput = function() {render(+this.value)}; // update on change
function render(v) {
ctx.clearRect(-0.5, -0.5, 600, 300);
ctx.strokeRect(0, 0, v, v);
ctx.fillText(v + " PPI", 10, 20);
// draw marks which should be 4 inches apart
ctx.fillRect(0, 0, 3, 150);
ctx.fillRect(96*4 * (v / 96), 0, 3, 150); // assuming 96 DPI base resolution
ctx.fillText("------ Should be 4 inches apart ------", 50, 140);
}
<label>Adjust so square below equals 1 inch:
<input type=range value=96 min=72 max=145></label>
<canvas width=600 height=300></canvas>
This example can of course be extended to take a vertical parameter as well as considering pixel aspect ratio (ie. retina displays) and scale.
You need to then build all your objects and graphics using a base scale, for example 96 DPI. Then use the relationship between the actual DPI and 96 DPI as a scale factor for all positions and sizes.
I need to draw 2 centimeters long line on screen on an Adobe Air application. I don't know how to do it!
Explanation:
I am getting parameters from another application say x centimeters, and that parameter is in centimeters.
I need to draw a circle exactly x centimeters from the top of the screen.
best regards
If I remember correctly, you won't be able to do it on desktop since AIR always returns 72DPI for the screen (I may be incorrect on that point, however). It is fairly easy to do on mobile, though, assuming AIR returns the proper DPI (retina iPads did not return the correct DPIs prior to AIR 3.3, I believe).
Basically, you convert inches to pixels simply by multiplying by the DPI.
var dpi:Number = Capabilities.screenDPI; //unnecessary to save local version, just easier to reference
var heightCM:Number = 5;
var widthCM:Number = 5;
var widthPixels:Number, heightPixels:Number;
var heightIn:Number = cmToInches( heightCM );
var widthIn:Number = cmToInches( widthCM );
widthPixels = widthIn * dpi;
heightPixels = heightIn * dpi;
function cmToInches( value:Number ):Number {
return value * .393701;
}
That will take a size (I built it for height and width, but you can adapt it to your needs) in centimeters, convert it to inches, and then convert it to pixels. You'd obviously want to turn that into a neat static Util method, but it would do the trick.
If you want, I created a Flex application last year to try and understand how AIR handles DPI differences. It just draws a red rectangle to a specific size on screen using on-screen sliders to determine the size (in inches). I don't have it here at work, but I could post the code when I get home.
Again, I do not believe this will work in desktop applications due to AIR always reporting 72 DPI. I hope I am wrong, but I do not believe I am.
I have a couple of AS3 games that I want to run in a flex mobile app. I put my original games into a single library and then added it to my mobile app. So far so good.
The problem I get is when the game starts it doesn't scale itself to the StageScaleMode.SHOW_ALL I have specified in the games.
I'm starting the games like this:
var game:MyGame = new MyGame();
var container:UIComponent = new UIComponent();
addElement(container);
container.addChild(game);
this.actionBarVisible = false;
I tried setting the same scale option to the stage in my mxml but it doesn't change anything.
Any ideas?
Thanks.
Mobile device screens have varying screen densities, or DPI (dots per inch). You can specify the DPI value as 160, 240, or 320, depending on the screen density of the target device. When you enable automatic scaling, Flex optimizes the way it displays the application for the screen density of each device.
For example, suppose that you specify the target DPI value as 160 and enable automatic scaling. When you run the application on a device with a DPI value of 320, Flex automatically scales the application by a factor of 2. That is, Flex magnifies everything by 200%.
To specify the target DPI value, set it as the applicationDPI property of the tag or tag in the main application file:
<s:ViewNavigatorApplication xmlns:fx="http://ns.adobe.com/mxml/2009"
xmlns:s="library://ns.adobe.com/flex/spark"
firstView="views.HomeView"
applicationDPI="160">
If you choose to not auto-scale your application, you must handle the density changes for your layout manually, as required.
Devices can have different screen sizes or resolutions and different DPI values, or densities.
Resolution is the number of pixels high by the number of pixels wide: that is, the total number of pixels that a device supports.
DPI is the number of dots per square inch: that is, the density of pixels on a device’s screen. The term DPI is used interchangeably with PPI (pixels per inch).
applicationDPI (if setted) specifies the target DPI of the application. Flex automatically applies a scale factor to fit good on another devices with different DPI value.
Capabilities.screenDPI is the specific DPI value of the current device.
runtimeDPI is similar to Capabilities.screenDPI. This value is the current device DPI rounded to one of the constants defined by the DPIClassification class (160, 240 and 320 DPI).
If you want to know the real dimensions (width and height) of a component on the current screens you need to work with the scale factor as:
var scaleFactor:Number = runtimeDPI / applicationDPI;
var currentComponentSize:int =componentSize.height * scaleFactor;
If you haven’t access to applicationDPI and runtimeDPI values, you can calculate the scaleFactor manually using Capabilities.screenDPI as:
// Copy the applicationDPI setted in your application. ie:
var _applicationDPI:int = 160;
var _runtimeDPI:int;
if(Capabilities.screenDPI < 200)
_runtimeDPI = 160;
else if(Capabilities.screenDPI >=200 && Capabilities.screenDPI < 280)
_runtimeDPI = 240
else if (Capabilities.screenDPI >=280)
_runtimeDPI = 320;
var scaleFactor:Number = _runtimeDPI / _applicationDPI;
var currentComponentSize:int =componentSize.height * scaleFactor;
http://www.francescoflorio.info/?p=234