/* RANDOM_G.C -- by Gary Neal, Jr.
 *
 * Draws random graphics of random colors.
 */

#include <stdlib.h> /* Required for rand() functions */
#include <dos.h>    /* Required for int86() functions */
#include <conio.h>  /* Required for keyboard functions */
#include <mem.h>    /* For memset & _fmemset functions */
#include <math.h>   /* For sine & cosine functions */

/* Video display definitions */
#define TEXT_MODE 0x03
#define VGA256    0x13

/* Define constants for screen dimensions */
#define ScreenWidth  (unsigned)320
#define ScreenHeight (unsigned)200

/* Create a pointer to video memory */
unsigned char far *videoMem = (unsigned char far *)0xA0000000L;

/* Function prototypes */
void SetVideoMode(int mode);
void SetPixel(int X, int Y, unsigned char C);
void FillScreen(int color);
void Line(int X1, int Y1, int X2, int Y2, unsigned char C);
void Circle(int xOffset, int yOffset, int radius, unsigned char C);

/* Our main program */
int main(void)
{
     while (kbhit()) getch();  /* Clear keyboard */

     SetVideoMode(VGA256);     /* Set VGA mode 13h */

     /* Random pixel demonstration */
     while (!kbhit())
          SetPixel(rand()%320, rand()%200, rand()%256);

     while (kbhit()) getch();  /* Clear keyboard */
     FillScreen(0);            /* Clear screen */

     /* Random line demonstration */
     while (!kbhit())
          Line(rand()%320, rand()%200, rand()%320, rand()%200, rand()%256);

     while (kbhit()) getch();  /* Clear keyboard */
     FillScreen(0);            /* Clear screen */

     /* Random circle demonstration */
     while (!kbhit())
          Circle(rand()%320, rand()%200, rand()%100, rand()%256);

     while (kbhit()) getch();  /* Clear keyboard */

     SetVideoMode(TEXT_MODE);  /* Set VGA mode 13h */

     return 0;                 /* Return without errors */
}

/* SetVideoMode function */
void SetVideoMode(int mode)
{
     union REGS regs;  /* Create register variables */

     regs.x.ax = mode; /* Set video mode */

     /* Call interrupt to complete the task */
     int86(0x10, &regs, &regs);
}

/* SetPixel function */
void SetPixel(int X, int Y, unsigned char C)
{
     videoMem[Y * 320 + X] = C;
}

/* FillScreen function */
void FillScreen(int color)
{
     /* Set all video memory to appropriate color */
     _fmemset(videoMem, color, ScreenWidth * ScreenHeight);
}

/* Line function
 *
 * Revised line function that will draw full lines
 * in any slope at any angle.
 */
void Line(int X1, int Y1, int X2, int Y2, unsigned char C)
{
    float currX, currY;           /* Current pixel to be plotted */
    float deltaX, deltaY, slope;  /* 2 deltas and slope */
    int tempVal;                  /* Holds temporary values */

    deltaX = X2 - X1;             /* Get value for delta X */
    deltaY = Y2 - Y1;             /* Get value for delta Y */

    if (deltaX < 0) deltaX = -deltaX;  /* Need absolute */
    if (deltaY < 0) deltaY = -deltaY;  /* values only.  */

    if (deltaY > deltaX) {

        /* |slope| > 1 */
        if (Y2 < Y1) {
            /* Swap coordinates, Y1 must be < Y2 */
            tempVal = Y2; Y2 = Y1; Y1 = tempVal;
            tempVal = X2; X2 = X1; X1 = tempVal;
        }

        /* Compute deltas and slope */
        deltaX = X2 - X1;
        deltaY = Y2 - Y1;

        /* Slope off the vertical axis */
        slope = deltaX / deltaY;

        /* Plot each pixel starting at (X1, Y1) */
        currX = X1;
        for (currY = Y1; currY <= Y2; currY++) {
            SetPixel((int)currX, (int)currY, C);
            currX += slope;    /* increment X by the slope */
        }
        return;

    } else if ((deltaY || deltaX) != 0) {

        /* |slope| < 1 */
        if (X2 < X1) {
            /* Swap coordinates, X1 must be < X2 */
            tempVal = X2; X2 = X1; X1 = tempVal;
            tempVal = Y2; Y2 = Y1; Y1 = tempVal;
        }

        /* Compute deltas and slope */
        deltaX = X2 - X1;
        deltaY = Y2 - Y1;

        /* Slope off the horizontal axis */
        slope = deltaY / deltaX;

        /* Plot each pixel starting at (X1, Y1) */
        currY = Y1;
        for (currX = X1; currX <= X2; currX++) {
            SetPixel((int)currX, (int)currY, C);
            currY += slope;    /* increment Y by the slope */
        }
        return;

    } else

        /* Set a single pixel because Y1 = Y2 and X1 = X2 */
        SetPixel(X1, Y1, C);
}

void Circle(int xOffset, int yOffset, int radius, unsigned char C)
{
     float xPlot, yPlot;     /* Current pixel being plotted */
     float angle, angleRad;  /* Current angle degrees & radiens */

     for (angle = 0.; angle < 360.; angle += 0.5) {

          /* Convert degrees to radiens */
          angleRad = angle * (3.141592654 / 180);

          /* Convert polar to rectangular coordinates */
          xPlot = (radius * cos(angleRad)) + xOffset;
          yPlot = (radius * sin(angleRad)) + yOffset;

          /* Check boundaries */
          if (xPlot < 0)
               xPlot = 0;
          else if (xPlot >= ScreenWidth)
               xPlot = ScreenWidth - 1;

          if (yPlot < 0)
               yPlot = 0;
          else if (yPlot >= ScreenHeight)
               yPlot = ScreenHeight - 1;

          /* Plot the pixel on the graphics screen */
          SetPixel((int)xPlot, (int)yPlot, C);
     }
}