Develop Reference

Fast pixel drawing in WPF

I would like to write a simple ray tracer using WPF. It is a learning project and thus I favour configurability over performance (otherwise I'd go for C++).
I still want relatively fast pixel drawing. A previous question on StackOverflow contains code to achieve this in WPF, by obtaining a GDI bitmap. From the relatively little I know about Windows programming,
GDI is slow
DirectX is fast
WPF uses DirectX underneath (not sure which parts of WPF though)
Is it possible to obtain pixel-level access using DirectX (not GDI) through the WPF Canvas (or similar)?
I will also consider suggestions for incorporating DirectX API calls within a WPF window (alongside other WPF controls) if that is possible.
Thanks in advance.

Interesting, but with raytracing, writing the pixels to the screen will (should) not be the slow part. You can use WriteableBitmap for the purpose, though. It's certainly quick enough for what you want.
http://msdn.microsoft.com/en-us/library/system.windows.media.imaging.writeablebitmap.aspx
(For info, I use it in this emu/IDE - http://0x10c-devkit.com/ - and it can refresh a low res display with great performance. There's the source to that on the github repository, the LEM1802 plugin.)
Ah, this bit: https://github.com/kierenj/0x10c-DevKit/blob/master/PluginAPI/NyaElektriska.LEM1802/GPU.cs - see UpdateDisplay.

Another solution is WriteableBitmapEx. It extends the builtin WriteableBitmap.

There is an open Source Project Called Direct Canvas wich is A hardware accelerated, 2D drawing API that supports vector graphics, multimedia files, extensible pixel shaders, blending modes and more!
http://directcanvas.codeplex.com/
Demo http://www.youtube.com/user/jdollah69#p/u

Native WPF vs. Custom DirectX for displaying large images

I need to speed up my image viewer, and wondering if I should be looking into creating my own DirectX control to do so.
My image viewer displays medical images. They can be pretty large. We're talking 55mb when it comes to mammography. The pixel data is 16bit greyscale stored in a ushort array. Without getting into the gory details, my current approach is loading the pixel data into an ImageSource, and using the WPF Image control.
I've never done anything with DirectX. Is it worth diving into it? Would it be any faster than the native WPF stuff? If so how significantly? Or, should I just forget about DirectX and look into areas where I can improve my current approach?
Before somebody says so, I know WPF utilize DirectX. I'm wondering If removing the WPF layer and writing the DirectX myself will improve performance.

I have some experience drawing multi-gigabyte satellite and chart imagery. Working with imagery around 55MB should probably work okay even without trying to optimize it too much. You haven't really given enough detail to recommend one alternative over the other, so I will give my opinion on the pros and cons.
Using 2D windows APIs will be the simplest to implement and should always be fast enough if you don't need to rotate and simply want to display an image and zoom and pan around. If you treat it as one large image the performance will not be as good when you zoom out if you are drawing with halftoning to give a nice smooth image. This is because it will effectively have to read all 55mb of image every time it draws.
To get around this performance issue you can make multiple bitmaps, effectively mip-mapping your image. As you zoom out you can pick the reduced resolution image closest to the resolution you are trying to draw . If you are not familiar with mip-mapping here is a Wikipedia link:
http://en.wikipedia.org/wiki/Mipmap
Implementing it with DirectX will be 10x as difficult. Different graphics hardware has different maximum texture sizes. Most likely you will need to break your image up in to multiple textures to draw and you will also have to keep track of render states, viewing matrices, etc.
However, if you do use DirectX, you can implement lots of real-time photo adjustments You can do real-time rotation by simply adjusting view matrices. You can do real-time contrast, brightness, gamma, and sharpness easily in a pixel shader.
There are two other API's I might suggest. If you are willing to limit yourself to Vista or later then Direct2D would be a little simpler than Direct3D. Also if you ever will need to implement it on a non-windows platform I would suggest using OpenGL instead. My current project is in Direct3D because a few years ago when we started it OpenGL was falling behind and I didn't forsee the popularity of Android devices. I now wish we had used OpenGL instead.

Try profiling to see where WPF is spending its time. Are you displaying the images at their native resolution? If not it might be worthwhile to do some preprocessing and create 1/2 resolution versions.

2D images to 3D view

I need to be able to generate a 3D perspective from a bunch of 2D images of a pipe.
Basically... We have written software that interprets combined data from laser and sonar units to give us an image slice from a section of pipe. These units travel through the pipe and scan the inside of the pipe every 100mm.
All of this is working great. My client now wants to take all these 2D image slices and generate a 3D view so they can "travel" through the pipe looking at defects etc.. that are picked up by the scans. We can see the defects in the 2D images but there can be hundreds of images in a single inspection - hence the requirement to be able to look through the pipe.
I am doing this in VS2010 on the .NET 4 platform in C#.
I am honestly clueless as to where to start here. I am not a graphics developer so this is all new territory to me. I see it as a great challenge but need some help kicking off - and a bit of direction.
Any help appreciated :)
Mike

Well, every 10cm isn't very detailed.. However, you need to scan the pixels of the pipe, creating a list of closed polygons, then just use a trianglestrip to connect one set to the next, all the way down the pipe.

Try to start with very basic 2d instead of full blown 3d rendering - may be good enough. Pipe when you look at it from inside can be represented as several trapeze. Assuming your images are small cylinder portions of a pipe - map each stripe to trapezoids (4 would be good start - easy to position) and draw than in circular pattern. You may draw several stripes this way at the same time. To move back/forward - just reassign images to trapezoids.
If you need full 3d - consider if WPF would work, if not - XNA or some OpenGL library will give you full 3d.

You don't specify the context, 100mm sample intervals may be sparse (a 1m pipe) or detailed (10km pipe). Nor do you specify how many sample points there are (number of cross sections and size of cross section image).
A simple way to show the data is to use voxels where each pixel on a cross section is treated as a cube and adjacent samples form adjacent cubes (think Minecraft). The result will look blocky but as it's an engineering / scientific application this is probably preferable. Interpolating the model to produce a smooth surface may hide defects or make areas appear to be defective. Also, rendering a cross section through a voxel is a bit easier than a polygon surface.

Web Page - 3d earthquake visualization - Silverlight?

I have never written any silverlight apps but I am looking to write a 3d viewer for earthquakes and have it run from my web site.
I would like to create a simple viewer so the user can change the "camera" ie their perspective. The view could contain up to 10,000 objects in the 3d space.
I want the ability to quickly view this - I have seen this on a Power Basic application and want to do this for the web.
I have a current web site at http://canterburyquakelive.co.nz for earthquakes in Canterbury New Zeaalnd and I want to learn the basics so that it can be more interactive.
I want to say for example (to start) place 2 objects in a "space" that I can define and move the camera in real time.
The system must support up to 10,000 objects in the end of the day.
Each object can be a simple circle - no need for special pixel shaders
I am unsure of the exact functionallity of the system at the moment so if I can find a tutorial that allows me to place someone (a circle) into a 3d world (space) and change the camera that would be good.
Any ideas appreciated - there seems to be so much about 3d and silverlight that I may be getting lost in the "gloss" of new features where I need some basics and I can learn and adapt over time.
** Added comment + image **
Basically I am waiting to create a page that look like this using Silverlight. But I am open to any technology.

I've never done 3D in silverlight so I can't exactly answer your question as asked but in general to display geographic markers in a 'real' 3D terrain is quite involved. At a minimum you're probably looking at:
Obtaining binary height data files (last time I looked, NASA gives this away)
Reading and interpreting said files to get 'bitmap' height data
Choosing and dealing with projections (e.g. UTM)
Deciding how to tesselate your bitmap height data
If you want it textured you'll need to also obtain satellite data for that, again converting or processing it to account for projection.
You could ignore the terrain height, but that may not simplify things depending on how 'bumpy' your terrain is.
For a pre-defined small enough area, you could perhaps pre-author a 3d model of the terrain in some 3D package but displaying your markers will still require a projection from long/lat into your 3D space, and you'll still need to know terrain height (unless you do mesh collision with the static model).
Rendering the markers is pretty straightforward by comparison, choose from:
Use a 3D model e.g. a 'pin head' (simple but not always visible)
Render a regular n-gon with 'viewer facing' polygons (resolution independent but maybe ugly)
Render a quad with a circle texture on it (low poly but what size texture to choose?)
There are probably libraries that do some or all of this for you, so if you are set on rolling your own then some of the things I've mentioned could form the basis for your search.
However, given what you've described of your site and situation I suspect you'd be better off avoiding all that work by using a pre-existing solution. E.g. the Google Earth API.

You could consider 3D web plugins that -granted- take you away from Silverlight but that might speed up your development process. I'm thinking in particular of e.g. the Blender 3D web plugin. I can understand the need to write your own viewer, but think twice before you re-invent the wheel. Good luck!

Is it reasonable to use OpenGL for desktop applications?

I've been writing a small desktop gadget-type application that displays scrolling text along the bottom of the screen (Similar to the old CNN news ticker), however the performance of GDI is just unsatisfactory (As high as 8-12% on a quad core and 20% on a single core) even after I've attempted to clean out bottlenecks.
I was considering using OpenGL instead to render everything, but I don't know if that is a reasonable option to require users to have hardware acceleration for a tiny app like this.
Does anybody have any input on this?

If you're comfortable with using OpenGL and your intended users are happy with the additional dependencies that OpenGL brings then I say go for it. :)
In terms of staying with GDI, I'd make sure you're rendering the text a few times as possible (through such techniques as rendering to bitmap and just scrolling that instead).
If neither one of those two options sounds appealing then there's always DirectX.

You could write the app in WPF and let WPF handle the acceleration for you (it's backed by DirectX).

I wouldn't want to install open gl for a program like that. You say that you "attempted" to eliminate the bottlenecks, but it does not sound like you succeeded. Like lzcd mentioned, there are other ways to scroll text than to repaint it constantly. Why not just draw to a bitmap and scroll that?