Pseudo-3D Rendering

This was a project I worked on because I wanted to try making some type of pseudo-3d using only 2d rendering in style with how older games had to simulate 3d graphics because of techical limitations. The project was made using c++ with nothing but the SDL library. With the SDL library I was able to use simple functions to render 2d squares (and sprites) to a simple window. I didn’t want to use anything more advanced since I wanted to try and recreate how older games used to implement this sort of effect.

How does it work?

Road Segments

The road being renderd is built up of what I called "Road Segments". One Road Segment is one horizontal line of the road. These are in simply just rendered rectangles. Before being rendered their width and height, or "thickness", is calculated based on how far away from the camera the segment is rendered.

Calculating Road Segment sizes

What this function does is, from the 3D world coordinates of each Road Segment and the Cameras position and settings, calculate out the correct screen-coordinates to render the Road Segment at.

It also calculates the Width and Height that the Road Segment should be rendered with, it does this using the distance between the Camera and the Road Segment, the dimensions of the camera and the FOV.

 
Scale = 1;
Width = 10000;
Height = 200;
    
Vector RoadSegment::Project(const Camera& Cam)
{
	Vector ScreenCoords;
	Vector3 CamCoordDif;
	Scale = Cam.FOV / (Position3D.Z - Cam.Position.Z);

	ScreenCoords.y = (1 - Scale * (Position3D.Y - Cam.Position.Y)) * (Cam.Height / 2);
	ScreenCoords.x = (Scale * (Position3D.X + Curve - Cam.Position.X)) * (Cam.Width / 2);

	ScreenCoords.y = ScreenCoords.y < 0 ? 0 : ScreenCoords.y;

	Width *= Scale;
	Height *= Scale;

	return ScreenCoords;
}

Curves and Hills

To make the hills and the road curve, I had to come up with a way to store a Map. This is so I can decide when and how the road should curve.

I did this by storing Map Segments in an array. Map segments contain 3 values: 

 
struct MapSegment
{
	int Length = 0;
	float Curvature = 0.f;
	float Hill = 0.f;
};

Length: For what distance / how long this segment should last.

Curvature: How much this segment should curve, and in what direction.

Hill: Same as Curvature, but for the vertical axis.

When drawing the road, the Road Segment's Position3D (world position) is determined based on what Map Segment we are currently in.

The proccess for calculating these are the exact same, the only difference is that the Y coordinate is calculated using the current Map Segment's Hill value, while the X coordinate uses the current Map Segment's Curvature value.

DistanceValue: The distance we've traveled along the map.

RenderDistance: How many Road Segments to render (to avoid melting the PC).

CurrentX/Y: The world coodrinate that the Road Segment should be at.

DeltaX/Y: How much the road curves / hills.

DeltaDeltaX/Y: How much the road's curve curves and hill hills.

CalculateRoadSegmentScreenPosition() Takes the Road Segment's world position and determines it's Screen Coordinates to be rendered at.

 
for (int i = DistanceValue; i < DistanceValue + RenderDistance; i++)
{
        DeltaX = RoadSegments[i].Curve;
        DeltaY = RoadSegments[i].Hill;
    
        CurrentX += DeltaDeltaX;
        RoadSegments[i].Position3D.X = CurrentX;
	DeltaDeltaX += DeltaX;
    
	CurrentY += DeltaDeltaY;
	RoadSegments[i].Position3D.Y = CurrentY;
	DeltaDeltaY += DeltaY;
    
	CalculateRoadSegmentScreenPositions(RoadSegments[i], i);
}

Lessons Learned

This was a small project that I made for fun in about 1-2 weeks. But this was one of the first things I made that had anything to do perspective projection, so I learned alot about different projection methods and how 3D rendering works.

The biggest issue this project has is that it's pretty slow, for example I can't use very high-res sprites and very few. This is because I render a ridiculous amount of Road Segments every frame, and on top of all that every Road Segment has both state and logic. One of the things I could do to improve this project in the future is to seperate out all the values of the Road Segments away from the actual object, this could lead to faster performance as I don't have to call functions on each Road Segment, but rather use data that is associated with the Road Segments outside of the object.