Pseudo-3D Road

#include <SFML/Graphics.hpp>
using namespace sf;

int width = 1024;
int height = 768;
int roadW = 2000;
int segL = 200; //segment length
float camD = 0.84; //camera depth

void drawQuad(RenderWindow &w, Color c, int x1, int y1, int w1, int x2, int y2, int w2)
{
    ConvexShape shape(4);
    shape.setFillColor(c);
    shape.setPoint(0, Vector2f(x1 - w1, y1));
    shape.setPoint(1, Vector2f(x2 - w2, y2));
    shape.setPoint(2, Vector2f(x2 + w2, y2));
    shape.setPoint(3, Vector2f(x1 + w1, y1));
    w.draw(shape);
}

struct Line
{
    float x, y, z; //3d center of line
    float X, Y, W; //screen coord
    float curve, spriteX, clip, scale;
    Sprite sprite;

    Line()
    {
        spriteX = curve = x = y = z = 0;
    }

    void project(int camX, int camY, int camZ)
    {
        scale = camD / (z - camZ);
        X = (1 + scale*(x - camX)) * width / 2;
        Y = (1 - scale*(y - camY)) * height / 2;
        W = scale * roadW  * width / 2;
    }

    void drawSprite(RenderWindow &app)
    {
        Sprite s = sprite;
        int w = s.getTextureRect().width;
        int h = s.getTextureRect().height;

        float destX = X + scale * spriteX * width / 2;
        float destY = Y + 4;
        float destW = w * W / 266;
        float destH = h * W / 266;

        destX += destW * spriteX; //offsetX
        destY += destH * (-1);    //offsetY

        float clipH = destY + destH - clip;
        if (clipH<0) clipH = 0;

        if (clipH >= destH) return;
        s.setTextureRect(IntRect(0, 0, w, h - h*clipH / destH));
        s.setScale(destW / w, destH / h);
        s.setPosition(destX, destY);
        app.draw(s);
    }
};


void Game_Start() {

    RenderWindow app(VideoMode(width, height), "Rado Tuning!");
    app.setFramerateLimit(60);

    Texture t[50];
    Sprite object[50];
    for (int i = 1;i <= 7;i++)
    {
        t[i].loadFromFile("images/" + std::to_string(i) + ".png");
        t[i].setSmooth(true);
        object[i].setTexture(t[i]);
    }

    Texture bg;
    bg.loadFromFile("images/bg.png");
    bg.setRepeated(true);
    Sprite sBackground(bg);
    sBackground.setTextureRect(IntRect(0, 0, 5000, 411));
    sBackground.setPosition(-2000, 0);

    std::vector<Line> lines;

    for (int i = 0;i<1600;i++)
    {
        Line line;
        line.z = i*segL;

        if (i>300 && i<700) line.curve = 0.5;
        if (i>1100) line.curve = -0.7;

        if (i<300 && i % 20 == 0) { line.spriteX = -2.5; line.sprite = object[5]; }
        if (i % 17 == 0) { line.spriteX = 2.0; line.sprite = object[6]; }
        if (i>300 && i % 20 == 0) { line.spriteX = -0.7; line.sprite = object[4]; }
        if (i>800 && i % 20 == 0) { line.spriteX = -1.2; line.sprite = object[1]; }
        if (i == 400) { line.spriteX = -1.2; line.sprite = object[7]; }

        if (i>750) line.y = sin(i / 30.0) * 1500;

        lines.push_back(line);
    }

    int N = lines.size();
    float playerX = 0;
    int pos = 0;
    int H = 1500;

    while (app.isOpen())
    {
        Event e;
        while (app.pollEvent(e))
        {
            if (e.type == Event::Closed)
                app.close();
        }

        int speed = 0;

        if (Keyboard::isKeyPressed(Keyboard::Right)) playerX += 0.1;
        if (Keyboard::isKeyPressed(Keyboard::Left)) playerX -= 0.1;
        if (Keyboard::isKeyPressed(Keyboard::Up)) speed = 200;
        if (Keyboard::isKeyPressed(Keyboard::Down)) speed = -200;
        if (Keyboard::isKeyPressed(Keyboard::Tab)) speed *= 3;
        if (Keyboard::isKeyPressed(Keyboard::W)) H += 100;
        if (Keyboard::isKeyPressed(Keyboard::S)) H -= 100;

        pos += speed;
        while (pos >= N*segL) pos -= N*segL;
        while (pos < 0) pos += N*segL;

        app.clear(Color(105, 205, 4));
        app.draw(sBackground);
        int startPos = pos / segL;
        int camH = lines[startPos].y + H;
        if (speed>0) sBackground.move(-lines[startPos].curve * 2, 0);
        if (speed<0) sBackground.move(lines[startPos].curve * 2, 0);

        int maxy = height;
        float x = 0, dx = 0;

        ///////draw road////////
        for (int n = startPos; n<startPos + 300; n++)
        {
            Line &l = lines[n%N];
            l.project(playerX*roadW - x, camH, startPos*segL - (n >= N ? N*segL : 0));
            x += dx;
            dx += l.curve;

            l.clip = maxy;
            if (l.Y >= maxy) continue;
            maxy = l.Y;

            Color grass = (n / 3) % 2 ? Color(16, 200, 16) : Color(0, 154, 0);
            Color rumble = (n / 3) % 2 ? Color(255, 255, 255) : Color(0, 0, 0);
            Color road = (n / 3) % 2 ? Color(107, 107, 107) : Color(105, 105, 105);

            Line p = lines[(n - 1) % N]; //previous line

            drawQuad(app, grass, 0, p.Y, width, 0, l.Y, width);
            drawQuad(app, rumble, p.X, p.Y, p.W*1.2, l.X, l.Y, l.W*1.2);
            drawQuad(app, road, p.X, p.Y, p.W, l.X, l.Y, l.W);
        }

        ////////draw objects////////
        for (int n = startPos + 300; n>startPos; n--)
            lines[n%N].drawSprite(app);

        app.display();
    }

}

int main()
{
    Game_Start();
    return 0;
}