Ken Heard composed on 2015-12-22 15:22 (UTC+0700):
I have a box with Debian Wheezy and TDE installed in it.
So do I. :-)
This is its motherboard: http://us.msi.com/product/motherboard/B85-G41-PC-Mate.html
What's yours? At least, tell which chipset and video you have via lspci output.
The GPU has three connectors, one DVI and two HDMI.
Mine has one each of VGA, DVI and HDMI.
I have two monitors connected to it.
Again do I. :-)
The diagonal measurement of one is 49 cm. It has a 1600x900 resolution and is connected to the box by a DVI cable.
Diagonal of my 1680x1050 connected via VGA cable is 56cm.
The other is a TV/monitor with a diagonal measurement of 124 cm (49 inches). It is connected to the box by HDMI.
Diagonal of my 1920x1080 connected by DVI to PC and HDMI to TV is 80cm.
The box recognizes its existence, but the display on it has the same resolution as the smaller monitor.
Can't say for sure why, but based on my experience, it should be a surmountable problem. Possibly HDCP is affecting behavior, or the HDMI cable. Have you tried any other cables? Cheaper HDMI cables are often a cause of otherwise inexplicable trouble.
It consequently uses only about 40-45% of the screen area, nor is it centred on the screen.
What's likely to be happening here is that the TV does not support the lower 1600x900 mode that Xorg automatically uses without being told otherwise for the larger resolution screen, so both falls back to a lower mode, and displays that mode without stretching, confining to the pixels on the 1920x1080 screen matching the actual mode used. If there is a video mode dictated on the kernel's cmdline (from bootloader), Xorg could be using it, as the Intel driver will do so unless told by xrandr or xorg.conf* to do otherwise.
It starts more or less from the upper left corner and leaves an L shaped unused black space on the bottom and right sides. The left side does not correspond to the left side of the screen; a strip on the left side of the display is seen on the smaller monitor but not on the large one.
IME, black/blank space is always at either bottom or right, but only in a screenshot, not on the screen output.
Sounds like neither display is being run in native mode. What is output from 'cat /proc/cmdline'? The whole of /var/log/Xorg.0.log may provide additional useful info.
Is it possible to create a display resolution larger than 1600x900 for the large monitor and properly centred on the screen, possibly using the ‘Monitor and Display’ feature of the TDE Control Centre?
Using TDE controls I've never tried. I always trust Xorg configuration to get screens the way I want them. Here are two such ways:
Over/Under: http://fm.no-ip.com/SS/KDE/tdeDesktop-1920x2130x120viaXrandr-iHaswell.jpg
Side by side: http://fm.no-ip.com/SS/KDE/tdeDesktop-3600x1080x120viaXorgdotconf-iHaswell.j...
In the over/under you can see the xrandr command responsible in the Konsole windows (and from whence it came, a personal creation). For the side by side I used this xorg.conf instead of xrandr: http://fm.no-ip.com/Share/Linux/xorg.conf-intel-vga1680x1050left-digi1920x10...
Of course the disparity between my screen sizes and yours are smaller, but they do have different native resolutions, and principles in controlling them are the same.
Note that in both my configurations I have forced logical DPI to a value that suits my needs. Via xrandr there are two ways to do this, --dpi and --fbmm. In xorg.conf, DisplaySize controls it. You can pick one that best suits your environment and display size disparity. If you don't, DPI will be forced to 96 on the lower resolution screen, and fall where happenstance puts it on the larger. Here's a file with examples, saving the trouble of calculating sizes to achieve many DPI possibilities: http://fm.no-ip.com/Share/Linux/DisplaySize
This is the web URL shown in the Firefox and SeaMonkey windows: http://fm.no-ip.com/Auth/dpi-screen-window.html
This is the script responsible for the output shown in the Konsole windows: http://fm.no-ip.com/Share/Linux/xfetch.sh
Hope this helps!