13. Drawing Examples

Dated: 12-05-2025

Drawing Table

A table consists of a table top and 4 legs, all rectangular.

Design

Constraints

• \(640 \times 480\) screen
• width = 20, length = 14, height = 10
• Screen top means \(y = 0\) and screen bottom means \(y = 480\)
• Table center is at the screen center

typedef struct {
    int x; 
    int y;
} Point;

Point points[4] = {
    {310, 233},
    {330, 233},
    {330, 247},
    {310, 247}
};

legLength = 10;

Point center = {
    (points[0].x + points[1].x) / 2,
    (points[1].y + points[2].y) / 2
};

void translate(int x, int y) { // move by (x, y)
    for (int i = 0; i < 4; i++) {
        points[i].x += x;
        points[i].y += y;
    }
}

void rotate(float theta) { // rotate by theta angle
    for (int i = 0; i < 4; i++) {
        points[i].x = center.x + (points[1].x - center.x) * cos(theta) - (points[i].y - center.y) * sin(theta);
        points[i].y = center.y + (points[1].x - center.x) * sin(theta) + (points[i].y - center.y) * cos(theta);
    }
}

void scale(int x, int y) { // scale by (x, y)
    for (int i = 0; i < 4; i++) {
        points[i].x = center.x + (points[i].x - center.x) * x;
        points[i].y = center.y + (points[i].y - center.y) * y;
    }

    legLength *= y;
}

void drawTable () {
    // Table Top
    line(points[0].x, points[0].y, points[1].x, points[1].y);
    line(points[1].x, points[1].y, points[2].x, points[2].y);
    line(points[2].x, points[2].y, points[3].x, points[3].y);
    line(points[3].x, points[3].y, points[0].x, points[0].y);

    // Legs
    line(points[0].x, points[0].y, points[0].x, points[0].y + legLength);
    line(points[1].x, points[1].y, points[1].x, points[1].y + legLength);
    line(points[2].x, points[2].y, points[2].x, points[2].y + legLength);
    line(points[3].x, points[3].y, points[3].x, points[3].y + legLength);
}