A triangle strip is a series of connected triangles, sharing vertices, allowing for faster rendering and more efficient memory usage for computer graphics. In OpenGL implementation, GL_TRIANGLE_STRIP draws a series of triangles using vertices v0, v1, v2, then v2, v1, v3 (note the order), then v2, v3, v4, and so on. The ordering is to ensure that the triangles are all drawn with the same orientation so that the strip can correctly form part of a surface
A triangle strip is a series of connected triangles, sharing vertices, allowing for faster rendering and more efficient memory usage for computer graphics. They are optimized on most graphics cards, making them the most efficient way of describing an object. There are two primary reasons to use triangle strips:
- Triangle strips increase code efficiency. After the first triangle is defined using three vertices, each new triangle can be defined by only one additional vertex, sharing the last two vertices defined for the previous triangle.
- Triangle strips reduce the amount of data needed to create a series of triangles. The number of vertices stored in memory is reduced from 3N to N+2, where N is the number of triangles to be drawn. This allows for less use of disk space, as well as making them faster to load into RAM.
OpenGL implementation
OpenGL has innate support for triangle strips using the glBegin(), glVertex*(), and glEnd() functions. To draw a triangle strip, glBegin() must be passed the argument GL_TRIANGLE_STRIP, which notifies OpenGL a triangle strip is about to be drawn. The glVertex*() family of functions specify the coordinates for each vertex in the triangle strip.
//Vertices below are in Clockwise orientation
//Default setting for glFrontFace is Counter-clockwise
glFrontFace(GL_CW);
glBegin(GL_TRIANGLE_STRIP);
glVertex3f( 0.0f, 0.0f, 0.0f ); //vertex 1
glVertex3f( 0.0f, 1.0f, 0.0f ); //vertex 2
glVertex3f( 1.0f, 0.0f, 0.0f ); //vertex 3
glVertex3f( 1.5f, 1.0f, 0.0f ); //vertex 4
glEnd();
Note that only one additional vertex is needed to draw the second triangle. In OpenGL, the order in which the vertices are specified is important so that surface normals are consistent.
Quoted directly from the OpenGL Programming Guide:
GL_TRIANGLE_STRIP Draws a series of triangles (three-sided polygons) using vertices v0, v1, v2, then v2, v1, v3 (note the order), then v2, v3, v4, and so on. The ordering is to ensure that the triangles are all drawn with the same orientation so that the strip can correctly form part of a surface.
