hmm, how do I explain...
Start from a 3D scenery... in order to render a 3D scene, the
computer must first calculate all the points that make up the dots
and lines of the scene, then it will apply the textures and
colours, adding in atmospheric effects like fog, rain (all these
are particle systems, which are made up of dots that the computer
will calculate also). So a typical 3D scene will be made up of tens
of thousands of points, the more as the more objects get into the
rendered picture.
So a 3D realtime rendered game will be running at least a 30 frames
per sec. So the computer will need to generate 30x such 'pictures'
per sec, which will be made up of millions of calculations.
A standard computer will be be already taxed with the processing of
the game itself (i.e the player controls, managing sounds, doing
other calculations), thus it will need a separate GPU (graphics
processing unit) to help lessen it's load. This is what graphic
cards come into play. They help the main cpu deal with all the
graphics. As for the quality of the graphic cards, the better and
more powerful the card, the better the quality of the rendered
picture. With a good graphics card can get very 'realistic' fog,
character renders etc. Vice versa, a poor quality graphics card
cannot render the picture that well cuz they still need to churn
out same amount of frames the game needs in order to run the game
smoothly. (This explains they 'jerkiness' of the game cuz the card
cannot handle it that well). So the better the graphics card, the
better the 3D quality and the more expensive the price.
