OpenGL Vertex Array

In OpenGL, if you are drawing an entity, you will generally use:

glBegin(GL_LINES);   glVertex3f(0.0f0.0f0.0f);    glVertex3f(1.0f0.0f0.0f);glEnd();

However, if the number of vertices is too many, this method requires frequent calls to the function and is inefficient. This will use the vertex array.

1. Enable vertex arrays

OpenGL is a state machine, before using a function, you must first turn on this function, after use, you can also close.

The code for enabling and closing the vertex array is as follows:

glEnableClientState(GL_VERTEX_ARRAY);   //启用glDisableClientState(GL_VERTEX_ARRAY);  //关闭

Where Gl_vertex_array is the type of array, there are eight kinds:

• Gl_vertex_array
• Gl_color_array
• Gl_second_color_array
• Gl_index_array
• Gl_normal_array
• Gl_fog_coordinate_array
• Gl_texture_coord_array
• Gl_flag_array

2. Specify an array

With the vertex array enabled, the next step is to specify: which array is the vertex array. The functions are as follows:

**void glvertexpointer (Glint size,
Glenum type,
Glsizei Stride,
const glvoid* pointer); * *

Parameters:

Size-the number of coordinates for each vertex, which must be 2, 3, or 4.

Type-the data type of the vertex coordinate, gl_short, gl_int, gl_float, or gl_double

Stride-the offset between two adjacent vertices, in bytes, and if 0, the surface vertices are tightly stored.

Pointer-the memory address of the first coordinate of the first item in the array.

In addition, Glcolorpointer, Glindexpointer, and so on, are used to specify other arrays.

Here's how to use it:

Glfloat vertexs[] = {0.0f,0.0f,0.0f,0.2f,0.0f,0.0f,                    -0.2f,0.0f,0.0f,0.0f,0.2f,0.0f,0.0f, -0.2f,0.0f,0.0f,0.0f,0.2f,0.0f,0.0f, -0.2f}; Glubyte indexs[] = {0,1,2,3,4,5,6};glenableclientstate (Gl_vertex_array);//enable vertex arrayGlenableclientstate (Gl_index_array);//enable indexed arraysGlvertexpointer (3, Gl_float,0, Vertexs);//Specify vertex arrayGlindexpointer (Gl_unsigned_byte,0, Indexs);//Specify an indexed array

3. Drawing

There are three functions for drawing.

void Glarrayelement (glint i);

Specify vertices from an indexed array, placed between Glbegin () and Glend (). For example:

glBegin(GL_POINTS);        glArrayElement(indexs[0]);        glArrayElement(indexs[1]);glEnd();

void Gldrawelements (glenum mode, Glsizei count, glenum type, const glvoid * indices);

Mode-primitive types, such as gl_points, Gl_lines

Count-Number of elements, index array exists in indices

Type-the data type of the indexed array must be gl_unsigned_byte, Gl_unsigned_short, or Gl_unsigned_int

Indices-indexed Array

Use methods such as:

glDrawElements(GL_POINTS,7,GL_UNSIGNED_BYTE,indexs);

void Gldrawarrays (Glenum mode, glint first, glsizei count);

For each enabled array (vertex array, array of colors, indexed array), draw elements from first to first+count-1 . Type is mode, for example Gl_points.

glDrawArrays(GL_POINTS,0,7);

OpenGL Vertex Array