title: “CS-421 Lab 3: Lego Models”
Note: Numerous links to Qt documentation pages that are no longer hosted at TrollTech have been removed.
Develop an OpenGL application that displays Lego models similar to those on the table in the illustration on your textbook’s cover.
You have been provided with an a utility class for drawing Lego blocks. The drawing routines make extensive use of OpenGL transformations. The geometries are based on library data from a Lego modeling application (LDraw, http://www.ldraw.org/), but do not take full advantage of OpenGL’s features. Feel free to modify this class (fix bugs, add block types, add support for other OpenGL features, improve the programming interface, etc.) in any way.
The following code will get you started using the Lego utility class in your paintGL() function. If you wish to render solids, be sure to make proper use of the depth buffer.
Lego::brick(); // default brick -- red, 2x4x1
glPushMatrix();
glTranslatef(Lego::lengthUnit, Lego::heightUnit, 0);
glRotatef(90, 0, 1, 0);
Lego::brick("yellow");
glPopMatrix();
Your renderings may be either wireframes or solids.
Your program must input models from a file. Each line of the file will specify a piece of Lego, unless it begins with a #, in which case it is a comment.
Here is a sample file for drawing the “sparse pyramid” on the cover of the textbook.
# origin (x, y, z) object_name [object_data ...] # origin - specifies the minimum x, y, and z coordinates of the object # For a standard block, the object format is # name(= block) color length width height 0 0 0 block green 4 2 1 6 0 0 block violet 4 2 1 12 0 0 block red 4 2 1 3 1 0 block red 4 2 1 9 1 0 block red 4 2 1 6 2 0 block yellow 4 2 1
Add 2 QSliders to your shell to allow the user to set the viewing latitude and longitude so that the model can be viewed from any angle. You will need to use signals and slots</a> that ultimately modify the modelview matrix. Mathematically, the viewing transforms happen after all the modeling transforms. In OpenGL, model and view transformations are combined into a single matrix and operations are coded from the left to the right (OpenGL uses right matrix multiplies instead of left matrix multiplies). This makes sense if you think of the transforms as moving the camera relative to the objects, but is precisely backwards if you think of the transforms as moving the objects relative to the camera; in CS-321, we focused on the later view. So, the viewing transform is coded as a starting point, and then objects are drawn which may manipulate the modelview matrix with their local modeling transforms, using the stack so that they leave the matrix in the same state when they’re done. This is how the Lego class works.
Demonstrate your working program to the professor (25% of grade) during or before the week 4 lab.
Your lab report need not be self-contained. This means that it is not necessary to restate the entire specification in your report.