The legacy device context is too coarse.

Question

Hi.

I have a Process Control system. It has a huge 2D workspace where all the logic is laid out. The 2D workspace is a coordinate system. You usually do not see the whole workspace at once, but rather some in-zoomed part of it focusing on some part of the controlled process. Such subsystem views are bookmarked into predefined named images (Power Generator1, Diesel Generator, Main lubrication pump etc).

This workspace interacts with many legacy MFC software components that individually contribute graphics onto the workspace (the device context is passed around to all contributors).

Now, one of the software components renders AutoCAD drawings onto the surface. However, the resolution of the device context is not sufficient for the details of this job. The device context logical resolution is unfortunately dictated by our own coordinate system, which at high zoom levels is quite different from the device units (pixels). For example, a line drawn using

DC.MoveTo(1,1); 
DC.LineTo(1,2);

.... will actually, even though it's drawn directly onto the device context by increment of just one logical unit, cover quite some distance on the screen. But the width of the line would still be only one device pixel. A circle looks high res, but its data (center point and radius) can only be done in coarse increments.

I have considered the following options: * When a predefined image is loaded and displayed, create a device context with a better suited resolution. The problem would then be that the other graphic providers interact with it using old logical units, which when used against the new DC would result in way too small and displaced graphical elements.

• I wonder if I can create some DC wrapper that accepts both kinds of coordinates through different APIs, which are then translated into high res coordinates internally.

• Is it possible to have two DCs with different logical/device unit ratio? And render them both to screen?

I mentioned that a circle is rendered beautifully with one pixel width even though it's placement and radius are restricted. Vertical lines are also rendered beautifully, even though the end points can only be given in coarse coordinates. This leads me to believe that it is technically possible to draw in an area that in DC logical coordinates could only be described in decimals.

Does anybody have any idea about what to do?

Answer 1

You need to scale your model, not the device context.

Answer 2

You could draw the high-def image to another DC in a new window and place that window over your low-res-drawing. Of course you have to handle clipping yourself.