How does a game actually get rendered?
By building each frame through a pipeline of stages, dozens of times a second — and understanding the stages explains why some settings are expensive and others nearly free.
The pipeline, simplified:
Geometry. The world is described as triangles. Each frame, their positions are transformed from world space into the camera's view and projected onto the screen.
Culling. Anything outside the camera's view, facing away, or hidden behind other geometry is discarded — the cheapest optimisation available, since not drawing something costs nothing.
Rasterisation. Triangles are converted into pixels.
Shading. For every pixel, a small program calculates its colour from textures, lighting, material properties and shadows. This is where most of the cost is, which is why resolution has such a large effect: twice the pixels means twice the shading work.
Post-processing — bloom, motion blur, depth of field, colour grading, anti-aliasing — applied to the finished image.
Why lighting dominates the difficulty. Real light bounces. Traditional rendering fakes this with precomputed lightmaps, which look excellent and cannot change, and with screen-space approximations that fail for anything off screen. Ray tracing simulates actual light paths, which is correct and expensive — hence its performance cost.
Why upscaling became standard. Rendering at lower resolution and reconstructing to a higher one, using motion vectors and prior frames, delivers most of the visual result for a fraction of the shading work. Frame generation goes further, creating intermediate frames — which raises the displayed frame rate without reducing input latency, since the generated frames contain no new input.
What each setting actually costs: resolution and shadow quality are usually the most expensive; texture quality is nearly free if you have enough video memory and catastrophic if you do not; draw distance costs both CPU and GPU; and anti-aliasing methods vary enormously.
Why the CPU matters too. It decides what to draw — physics, AI, and issuing draw calls. A CPU bottleneck shows as poor frame rate that does not improve when you lower graphics settings, which is the diagnostic worth knowing.