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August 1999 Programmer's Challenge
3D FlyBy
Mail solutions to:
progchallenge@mactech.com
Due Date: 11:59pm ET, Thursday, 12 August 1999
Some of the people who have recently written to suggest possible Challenge problems have asked for Challenges that are more specific to the Macintosh. Well, not everyone is actually that subtle about it. One writer lamented "yet another plain-vanilla Challenge that could just as well have appeared in a Linux or Windows programming magazine". Ouch!! Since this column is based on demonstrating efficient performance, many of the problems naturally carry over to other platforms. But the writer has a point, and this month’s Challenge will have more to do with the MacOS.
Back in April, readers were asked to find a path through three-dimensional terrain that minimized elevation change. This month, you’ll also be dealing with 3D terrain, but you’ll be flying over it, and displaying a perspective view of that terrain. In the process, you’ll have the opportunity to learn a little about QuickDraw3D.
The prototype for the code you should write is:
#include <QD3D.h>#include <QD3DLight.h>#include <QD3DCamera.h>
#include <Windows.h>
#if defined(__cplusplus)
extern "C" {
#endif
typedef struct MyTriangles {
long pointIndices[3];
TQ3ColorRGB triangleColor;
} MyTriangles;
void InitFlyBy(
CWindowPtr theWindow,
long numPoints,
const TQ3Point3D thePoints[],
long numTriangles,
const MyTriangles theTriangles[],
const TQ3ViewAngleAspectCameraData perspectiveData,
// perspectiveData.cameraData.range.hither = 0.0;
// perspectiveData.cameraData.range.yon = 1000.0
// perspectiveData.cameraData.viewPort.origin.x = -1.0
// perspectiveData.cameraData.viewPort.origin.y = 1.0
// perspectiveData.cameraData.viewPort.width = 2.0
// perspectiveData.cameraData.viewPort.height = 2.0
// perspectiveData.fov = 1.0
// perspectiveData.aspectRatioXToY =
// (float) (theWindow->portRect.right - theWindow->portRect.left) /
// (float) (theWindow->portRect.bottom - theWindow->portRect.top)
const TQ3ColorRGB backgroundColor
// color of background
);
void GenerateView(
TQ3CameraPlacement viewPoint
);
void TermFlyBy(void);
#if defined(__cplusplus)
}
#endif
Your code consists of three routines: InitFlyBy. called once for each terrain map; GenerateView, called repeatedly with different view positions as you fly through the terrain; and TermFlyBy, called at the end of each flight.
InitFlyBy is given everything needed to describe the scene to be generated except the viewPoint. The terrain consists of numPoints terrain coordinates provided in thePoints. The terrain is divided into numTriangles triangles, provided in theTriangles, each of which is described by 3 pointIndices into thePoints array, plus a color for the triangle.
Each time GenerateView is called, the terrain should be displayed in theWindow from the viewPoint using the projection information provided in perspectiveData. The projection will be a perspective, as opposed to an orthographic, projection, described using the TQ3ViewAngleAspectCameraData structure. The range, viewPort, fov, and aspectRationXToY elements of that structure are guaranteed to be defined using the simplifying values shown in the prototype commentary above.
Triangles should be displayed in the triangleColor, and areas of the scene not included in theTriangles should be displayed in the backgroundColor.
To optimize your code, you can rely on the fact that the viewPoint cameraLocation provided on successive calls to GenerateView will not change very much, simulating an actual flight. Similarly, the viewPoint pointOfInterest that determines the viewing direction, and the viewPoint upVector that governs orientation will not change by large amounts. They will change as the simulated flying machine banks and turns to avoid terrain.
A more realistic FlyBy Challenge would include one or more light sources, an illumination model, and the projection of shadows. For simplicity, we’ll omit those minor details. We’ll also allow you to fly without worrying about intersecting the terrain ("crashing") — the test code won’t do that.
TermFlyBy should deallocate any dynamically allocated memory. Remember, your solutions need to properly initialize and clean up after themselves so they can be executed repeatedly.
Look here for information on QuickDraw3D data structures.
The winner will be the solution that accurately depicts multiple flights through terrain using the least amount of execution time. This will be a native PowerPC Challenge, using the latest CodeWarrior environment. Solutions may be coded in C, C++, or Pascal.
Test code for this Challenge is available.
You can get a head start on the Challenge by reading the
Programmer's Challenge mailing list. It will be posted to the list on
or before the 12th of the preceding month. To join, send an email to
listserv@listmail.xplain.com
with the subject "subscribe challenge-A". You can also join the
discussion list by sending a message with the subject "subscribe
challenge-D".
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