This is a simple narrative description of the texture application included with the Lumen library as a demo.

The texture demo accepts one command-line parameter, which is the name of an image in BMP format, or netpbm's portable bitmap, portable greymap, or portable pixmap format (PBM, PGM, or PPM). Yes yes, we'll be adding more formats shortly. One BMP and one PPM image are included in the data directory for you to use with this demo. You can convert other images to BMP or PPM format using any of a number of free tools, like the netpbm toolkit, GIMP, or ImageMagick. You invoke texture by typing its name followed by an image name, like ./texture ../data/ppm-test-8.ppm if you're sitting in the bin directory, or bin/texture data/bmp-test-1.bmp if you're in the lumen directory. When run, texture creates a window the same size as your image, so for best results, use images that are smaller than your screen. (The actual image is displayed on a rectangle that's smaller, so it has room to rotate.)

The window should have a light grey background with a slowly rotating rectangle in it which has your image mapped on it. It should complete one full rotation every 15 seconds, since it advances the rotation one degree every frame, and should run at 24 frames per second. Terminate it by pressing any key, or closing the window.

Incidentally, the image included in the demo directory named ppm-test-8.ppm, is a public-domain photo of the Aurora Borealis, also known as the Northern Lights. It was taken in 2005 near Eielson Air Force Base, Alaska by Senior Airman Joshua Strang of the United States Air Force. The bmp-test-1.ppm image is a public-domain raytraced image from Wikimedia Commons.

The texture demo is an enhancement of the spinner demo, mainly intended to show how to use the Lumen.Image package. It's getting closer to what a real Lumen app might typically look like, though it's still very basic.

Like in spinner, creating a double-buffered rendering context (by allowing the default Animated => True in Lumen.Window.Create) is actually necessary here in order to get smooth animation. And as with all d-b contexts, we call Lumen.Window.Swap after we've finished our scene, so as to sort of "publish" it to the user.

Event-wise, texture is just the same as spinner, using Lumen.Events.Animate.Select_Event for its event loop.

Much of the rest of the app is similar to spinner, with a few additions and alterations. First, instead of drawing a shaded square, it uses OpenGL's texturing facility to draw a rectangle with the selected image drawn on it. Second, it sets up a real 3D frustum instead of using the much simpler 2D orthographic projection used by all previous demos. Third, now that it has real 3D space to move in, it rotates the square along two axes instead of just one.

Last Updated: 14 Dec 2011 09:32:32