Demo program A

Bounding Cube

Here, in the sense of summarizing the flow up to now, I will introduce a slightly complicated program for displaying polygons using the functions that have appeared so far.

So far, we have explained the following:

Drawing: Polygon definition (Chapter 2)
Light source: Setting the light source and changing the polygon surface due to the light source (Chapter 3)
Coordinate system: Coordinate system in Sega Saturn (Chapter 4)
Modeling transformations: rotating, moving, scaling objects, etc. (Chapter 4)
Drawing area: Window and clipping (Chapter 4)

These are relatively common ideas in 3D graphics, regardless of the hardware (of course, the functions used are different...).
Please understand these before proceeding to the next chapter.
From the next chapter onwards, we will mainly explain the ideas and special functions unique to the Sega Saturn.

The demo program "demo_A" uses a combination of SGL library functions from drawing to coordinate transformation.
In the demo, a small cubic polygon bounces around a room represented by cubic polygons with all faces facing inward (and not drawn when viewed from the outside).
Collision detection between the room and the small cube is processed using simple conditional branching (XYZ coordinate values).

Figure A-1 Operation image of demo A

List A-1 demo_A: Demo program A

/*------------------------------------------------ ----------------------*/
/* Cube Action */
/*------------------------------------------------ ----------------------*/
#include "sgl.h"

#define REFLECT_EXTENT toFIXED(85.0)
#define XSPD toFIXED(1.5)
#define YSPD toFIXED(2.0)
#define ZSPD toFIXED(3.0)

extern PDATA PD_PLANE1, PD_PLANE2;

void ss_main(void)
{
	static ANGLE ang1[XYZ], ang2[XYZ];
	static FIXED pos1[XYZ], pos2[XYZ], delta[XYZ], light[XYZ];

	slInitSystem(TV_320x224, NULL, 1);
	slPrint("demo A", slLocate(9,2));

	ang1[X] = ang1[Y] = ang1[Z] = DEGtoANG(0.0);
	ang2[X] = ang2[Y] = ang2[Z] = DEGtoANG(0.0);
	pos1[X] = pos2[X] = toFIXED( 0.0);
	pos1[Y] = pos2[Y] = toFIXED( 0.0);
	pos1[Z] = pos2[Z] = toFIXED(100.0);
	delta[X] = XSPD, delta[Y] = YSPD, delta[Z] = ZSPD;
	light[X] = slSin(DEGtoANG( 30.0));
	light[Y] = slCos(DEGtoANG( 30.0));
	light[Z] = slSin(DEGtoANG(-30.0));

	while(-1){
		slLight(light);
		slPushMatrix();
		{
			slTranslate(pos1[X], pos1[Y], pos1[Z] + toFIXED(270.0));

			pos1[X] += delta[X];
			pos1[Y] += delta[Y];
			pos1[Z] += delta[Z];

			if(pos1[X]> REFLECT_EXTENT){
				delta[X] = -XSPD, pos1[X] -= XSPD;
			} else if(pos1[X]< -REFLECT_EXTENT){
				delta[X] = XSPD, pos1[X] += XSPD;
			}
			if(pos1[Y]> REFLECT_EXTENT){
				delta[Y] = -YSPD, pos1[Y] -= YSPD;
			} else if(pos1[Y]< -REFLECT_EXTENT){
				delta[Y] = YSPD, pos1[Y] += YSPD;
			}
			if(pos1[Z]> REFLECT_EXTENT){
				delta[Z] = -ZSPD, pos1[Z] -= ZSPD;
			} else if(pos1[Z]< -REFLECT_EXTENT){
				delta[Z] = ZSPD, pos1[Z] += ZSPD;
			}

			slRotX(ang1[X]);
			slRotY(ang1[Y]);
			slRotZ(ang1[Z]);
			ang1[X] += DEGtoANG(3.0);
			ang1[Y] += DEGtoANG(5.0);
			ang1[Z] += DEGtoANG(3.0);
			slPutPolygon(&PD_PLANE1);
		}
		slPopMatrix();
		
		slPushMatrix();
		{
			slTranslate(pos2[X], pos2[Y], pos2[Z] + toFIXED(170.0));
			slRotY(ang2[Y]);
			slRotX(ang2[X]);
			slRotZ(ang2[Z]);
			slPutPolygon(&PD_PLANE2);
		}
		slPopMatrix();

		slSynch();
	}
}

Flow A-1 sample_1_6: Flowchart of demo program A

In the next chapter, we will provide a more in-depth explanation, starting with the hierarchical matrix.
In particular, the concept of hierarchical structure using stacks is an important factor in 3D graphics, so please read it carefully or refer to specialized books to understand it.