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Prezentace Camera analogy_Hlopko Marcel

Y04A2Z - Anglický jazyk 2-1

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glEnd();
glFlush();
UpdateTheWindow();
}
InitializeAWindow() command initializes a window on the screen. This command is different on different window systems (X window systém on Solaris, Microsoft Windows etc.). Next two commands will set the background color to black and will clear the window (to black). GlColor3f sets what color to use for drawing objects. In this case, color is white. GlOrtho specifies a coordinate system. Next calls that are bracketed by glStart() and glEnd() define the object to be drawn. In our case a polygon with 4 vertices is drawn. GlFlush() ensures that drawing commands are executed, not only stored in buffer and waiting for additional commands. UpdateTheWindow() is also dependable on an operating system.
At the highest level of abstraction, there are only three basic drawing operations: clearing the window, drawing a geometric object and drawing a raster object. Raster objects are things like two dimensional images (as you could see in old action games like Duke Nukem 3d), bitmaps, character fonts.

This image has been drawn using a similar (but far more complicated) code as you saw before. Everything you can see consists of points, lines, and polygons. Nothing more. There is a round table, many things with curved surface. How to do that using straight lines? It turns out that all the curved lines and surfaces you’ve seen are approximated by large numbers of little flat polygons or straight lines, in the same way that the globe is constructed from a large set of rectangular blocks. The globe doesn't appear to have a smooth surface, because the blocks are relatively large compared to the globe.

What are points, lines and polygons?

You have a fairly good idea what a point, line and polygon are. The OpenGL meaning is similar, but not the same. One difference comes from the limitation of computer-based calculations that are finite precision, and have round-off errors. Another limitation arises from a raster graphic display. The smallest displayable unit is a pixel. And the pixel is larger than an infinitely small point or infinitely thin line.
A point is represented as a vertex. In OpenGL a term line refers to a line segment, not as mathematicians' version that extends to infinity.Polygons are the areas enclosed by single closed loops of line segments. OpenGL polygons must be convex. That means that if two points are in interior, the line segment must be in interior too. Polygons don't have to be in a plane. Imagine a four-point quadrilateral where the points are slightly out of plane. And now look at it almost edge-on. You can get a non-simple polygon. That is why triangles are used. Three points always lie on the same plane.

Other choices – DirectX

DirectX is almost the same thing as OpenGL. It is widely used in the developm

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Vloženo: 26.04.2009

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