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50-06.md
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------------------------ --------------------------------- --------------------
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[Previous](50-05.html) [Table of Contents](index.html) [Next](50-07.html)
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------------------------ --------------------------------- --------------------
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**LISTING 50.5 L50-5.C**
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/* Simple 3-D drawing program to view a polygon as it rotates in
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Mode X. View space is congruent with world space, with the
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viewpoint fixed at the origin (0,0,0) of world space, looking in
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the direction of increasingly negative Z. A right-handed
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coordinate system is used throughout.
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Tested with Borland C++ in the small model. */
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#include <conio.h>
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#include <stdio.h>
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#include <dos.h>
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#include <math.h>
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#include “polygon.h”
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void main(void);
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/* Base offset of page to which to draw */
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unsigned int CurrentPageBase = 0;
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/* Clip rectangle; clips to the screen */
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int ClipMinX=0, ClipMinY=0;
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int ClipMaxX=SCREEN_WIDTH, ClipMaxY=SCREEN_HEIGHT;
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/* Rectangle specifying extent to be erased in each page */
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struct Rect EraseRect[2] = { {0, 0, SCREEN_WIDTH, SCREEN_HEIGHT},
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{0, 0, SCREEN_WIDTH, SCREEN_HEIGHT} };
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/* Transformation from polygon’s object space to world space.
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Initially set up to perform no rotation and to move the polygon
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into world space -140 units away from the origin down the Z axis.
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Given the viewing point, -140 down the Z axis means 140 units away
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straight ahead in the direction of view. The program dynamically
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changes the rotation and translation. */
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static double PolyWorldXform[4][4] = {
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{1.0, 0.0, 0.0, 0.0},
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{0.0, 1.0, 0.0, 0.0},
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{0.0, 0.0, 1.0, -140.0},
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{0.0, 0.0, 0.0, 1.0} };
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/* Transformation from world space into view space. In this program,
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the view point is fixed at the origin of world space, looking down
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the Z axis in the direction of increasingly negative Z, so view
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space is identical to world space; this is the identity matrix. */
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static double WorldViewXform[4][4] = {
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{1.0, 0.0, 0.0, 0.0},
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{0.0, 1.0, 0.0, 0.0},
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{0.0, 0.0, 1.0, 0.0},
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{0.0, 0.0, 0.0, 1.0}
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};
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static unsigned int PageStartOffsets[2] =
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{PAGE0_START_OFFSET,PAGE1_START_OFFSET};
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int DisplayedPage, NonDisplayedPage;
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void main() {
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int Done = 0;
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double WorkingXform[4][4];
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static struct Point3 TestPoly[] =
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{{-30,-15,0,1},{0,15,0,1},{10,-5,0,1}};
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#define TEST_POLY_LENGTH (sizeof(TestPoly)/sizeof(struct Point3))
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double Rotation = M_PI / 60.0; /* initial rotation = 3 degrees */
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union REGS regset;
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Set320x240Mode();
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ShowPage(PageStartOffsets[DisplayedPage = 0]);
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/* Keep rotating the polygon, drawing it to the undisplayed page,
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and flipping the page to show it */
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do {
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CurrentPageBase = /* select other page for drawing to */
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PageStartOffsets[NonDisplayedPage = DisplayedPage ^ 1];
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/* Modify the object space to world space transformation matrix
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for the current rotation around the Y axis */
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PolyWorldXform[0][0] = PolyWorldXform[2][2] = cos(Rotation);
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PolyWorldXform[2][0] = -(PolyWorldXform[0][2] = sin(Rotation));
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/* Concatenate the object-to-world and world-to-view
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transformations to make a transformation matrix that will
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convert vertices from object space to view space in a single
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operation */
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ConcatXforms(WorldViewXform, PolyWorldXform, WorkingXform);
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/* Clear the portion of the non-displayed page that was drawn
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to last time, then reset the erase extent */
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FillRectangleX(EraseRect[NonDisplayedPage].Left,
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EraseRect[NonDisplayedPage].Top,
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EraseRect[NonDisplayedPage].Right,
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EraseRect[NonDisplayedPage].Bottom, CurrentPageBase, 0);
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EraseRect[NonDisplayedPage].Left =
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EraseRect[NonDisplayedPage].Top = 0x7FFF;
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EraseRect[NonDisplayedPage].Right =
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EraseRect[NonDisplayedPage].Bottom = 0;
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/* Transform the polygon, project it on the screen, draw it */
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XformAndProjectPoly(WorkingXform, TestPoly, TEST_POLY_LENGTH,9);
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/* Flip to display the page into which we just drew */
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ShowPage(PageStartOffsets[DisplayedPage = NonDisplayedPage]);
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/* Rotate 6 degrees farther around the Y axis */
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if ((Rotation += (M_PI/30.0)) >= (M_PI*2)) Rotation -= M_PI*2;
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if (kbhit()) {
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switch (getch()) {
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case 0x1B: /* Esc to exit */
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Done = 1; break;
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case ‘A’: case ‘a’: /* away (-Z) */
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PolyWorldXform[2][3] -= 3.0; break;
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case ‘T’: /* towards (+Z). Don’t allow to get too */
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case ‘t’: /* close, so Z clipping isn’t needed */
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if (PolyWorldXform[2][3] < -40.0)
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PolyWorldXform[2][3] += 3.0; break;
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case 0: /* extended code */
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switch (getch()) {
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case 0x4B: /* left (-X) */
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PolyWorldXform[0][3] -= 3.0; break;
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case 0x4D: /* right (+X) */
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PolyWorldXform[0][3] += 3.0; break;
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case 0x48: /* up (+Y) */
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PolyWorldXform[1][3] += 3.0; break;
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case 0x50: /* down (-Y) */
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PolyWorldXform[1][3] -= 3.0; break;
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default:
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break;
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}
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break;
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default: /* any other key to pause */
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getch(); break;
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}
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}
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} while (!Done);
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/* Return to text mode and exit */
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regset.x.ax = 0x0003; /* AL = 3 selects 80x25 text mode */
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int86(0x10, ®set, ®set);
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}
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------------------------ --------------------------------- --------------------
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[Previous](50-05.html) [Table of Contents](index.html) [Next](50-07.html)
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------------------------ --------------------------------- --------------------
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* * * * *
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Graphics Programming Black Book © 2001 Michael Abrash
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