GS_line.cpp

#include "proj.h"

void drawGSPoint(point p, float i, int color) {
    i = 1-i;
    if (i < 0) {i = 0;}

    // set point color
    float red_c = 0.0f, green_c = 0.0f, blue_c = 0.0f;
    if (color == GS_RED) red_c = 1.0f;
    else if (color == GS_GREEN) green_c = 1.0f;
    else if (color == GS_BLUE) blue_c = 1.0f;
    else {red_c=1.0f; green_c=1.0f; blue_c=1.0f;}
    glColor3f(red_c * i, green_c * i, blue_c * i); 

	// set point size and plot
    glBegin(GL_POINTS);
        glPointSize(1);
        glVertex2d(p.x, p.y);
    glEnd();
}

int negate(int self, int other) {
    return 2 * other - self;
}

point swap(int x, int y, int x0, int y0) {
    return {x0 + (y-y0), y0 + (x-x0)};
}

point transformPoint(int x, int y, double s, int x0, int x1, int y0) {
    if (x0<=x1) {
        if (s > 1) return swap(x, y, x0, y0);
        else if (-1 <= s && s < 0) return {x, negate(y, y0)}; 
        else if (s < -1) {
            point temp = swap(x, y, x0, y0);
            return {temp.x, negate(temp.y, y0)};
        }
    } else {
        if (s >= 0 && s <= 1) return {negate(x,x0), negate(y,y0)};
        else if (1 < s) {
            point temp = swap(x, y, x0, y0);
            return {negate(temp.x, x0), negate(temp.y, y0)};
        }
        else if (-1 <= s && s < 0) return {negate(x,x0), y};
        else {
            point temp = swap(x, y, x0, y0);
            return {negate(temp.x, x0), temp.y};
        }
    }
    return {x, y};
}

point transform_p1(int x0, int y0, int x1, int y1, double s) {
    if (x0<=x1) {
        if (s > 1) return swap(x1, y1, x0, y0);
        else if (-1 <= s && s < 0) return {x1, negate(y1, y0)}; 
        else if (s < -1) {
            point temp = swap(x1, y1, x0, y0);
            return {negate(temp.x, x0), temp.y};
        }
    } else {
        if (s >= 0 && s <= 1) return {negate(x1, x0), negate(y1, y0)};
        else if (1 < s) {
            point temp = swap(x1, y1, x0, y0);
            return {negate(temp.x, x0), negate(temp.y, y0)};
        }
        else if (-1 <= s && s < 0) return {negate(x1, x0), y1};
        else {
            point temp = swap(x1, y1, x0, y0);
            return {temp.x, negate(temp.y, y0)};
        }
    }
    return {x1, y1};
}

int checkStipple(unsigned short &s) {
    if ((s & 1) == 1) {
        s = (s >> 1) | 0b1000000000000000;
        return 1;
    } else {
        s = s >> 1;
        return 0;
    }
}

void GSLine(int x0, int y0, int x1, int y1, int color, unsigned short stipple, unsigned int thickness) {
    int x0T = x0, x1T = x1, y0T = y0, y1T = y1;
    float dxT = x1-x0, dyT = y1-y0; // calculate and save true slope
    double slope = dyT/dxT;
    
    point p1 = transform_p1(x0, y0, x1, y1, slope);// transform initial points

    float dx = p1.x-x0, dy = p1.y-y0; // redo dx and dy calculations

    float d = 2 * dy - dx;
    float deltaE = 2 * dy, deltaNE = 2 * (dy-dx);
    
    float tvdx = 0;
    float L = 2.0 * sqrt(dx * dx + dy * dy);
    float Dyp, DypPlus, DypMinus;
    
    int x = x0, y = y0;

    if (checkStipple(stipple)) {
        drawGSPoint(transformPoint(x, y, slope, x0T, x1T, y0T), 0, color);
        for (int i = 1; i < thickness; i++) {
            drawGSPoint(transformPoint(x, y+i, slope, x0T, x1T, y0T), 0, color);
            drawGSPoint(transformPoint(x, y-i, slope, x0T, x1T, y0T), 0, color);
        }
        drawGSPoint(transformPoint(x, y+thickness, slope, x0T, x1T, y0T), .5, color);
        drawGSPoint(transformPoint(x, y-thickness, slope, x0T, x1T, y0T), .5, color);
    }

    while (x < p1.x) {

        if (d <= 0){ // E
            tvdx = d+dx;
            d = d + deltaE;
        } else { // NE
            tvdx = d-dx;
            d = d + deltaNE;
            y++;
        }
        x++;
        Dyp = abs((tvdx)/L);
        DypPlus = abs((2*dx - tvdx)/L);
        DypMinus = abs((2*dx + tvdx)/L);
        if (checkStipple(stipple)) {
            drawGSPoint(transformPoint(x, y, slope, x0T, x1T, y0T), 0, color);
            for (int th = 1; th < thickness; th++) {
                drawGSPoint(transformPoint(x, y+th, slope, x0T, x1T, y0T), 0, color);
                drawGSPoint(transformPoint(x, y-th, slope, x0T, x1T, y0T), 0, color);
            }
            drawGSPoint(transformPoint(x, y+thickness, slope, x0T, x1T, y0T), DypPlus, color);
            drawGSPoint(transformPoint(x, y-thickness, slope, x0T, x1T, y0T), DypMinus, color);
        }
    }
}