Article Directory
Function glDrawArrays ()
glDrawArrays(type, startIndex, count);Drawing a triangle
of which type is divided into:
- GL_TRIANGLE
This understanding is the simplest. Each drawing is a three vertices of a triangle. But this will be relatively large vertex array length. - GL_TRIANGLE_STRIP
- GL_TRIANGLE_FAN
GL_TRIANGLE_STRIP
strip: strip, the strip means
to select it when drawing pattern extending in one direction.
N-number of set top set; the first three vertices constituting the first triangle counterclockwise.
Thereafter, the n vertices,
- When n is an even number:
(. 1-n, n-2, n) as n is 4, represents the four vertices, is to use a third time, the second and fourth vertices constituting a triangle counterclockwise- When n is odd:
(n-2,. 1-n, n)
GL_TRIANGLE_FAN
fan: sector
select it in drawing fan circular.
The initial vertex needs to be the center of the sector, the first three vertices of a first triangle constituting counterclockwise.
From the third starting vertex satisfied, that is, (n, circle, n-1)
The initial vertex
In OpenGL, we need to draw counter-clockwise. Therefore, in the second type GL_TRIANGLE_STRIP, the vertex direction of the front three generally like this:
- First and second vertex, from top to bottom; the second and third vertices from left to right.
On the contrary it is also true, i.e., the first and second vertex, from the bottom up; the second and third vertex from right to left. - First and second vertex, left to right; the second and third vertex, from the bottom up.
Also, conversely, the first and second vertex, from right to left; downwardly from the second and third vertex.
