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glDrawArrays

Name

glDrawArrays — render primitives from array data

C Specification

void glDrawArrays(GLenum mode,
GLint first,
GLsizei count);

Parameters

mode

Specifies what kind of primitives to render. Symbolic constants GL_POINTS, GL_LINE_STRIP, GL_LINE_LOOP, GL_LINES, GL_LINE_STRIP_ADJACENCY, GL_LINES_ADJACENCY, GL_TRIANGLE_STRIP, GL_TRIANGLE_FAN, GL_TRIANGLES, GL_TRIANGLE_STRIP_ADJACENCY and GL_TRIANGLES_ADJACENCY are accepted.

first

Specifies the starting index in the enabled arrays.

count

Specifies the number of indices to be rendered.

Description

glDrawArrays specifies multiple geometric primitives with very few subroutine calls. Instead of calling a GL procedure to pass each individual vertex, normal, texture coordinate, edge flag, or color, you can prespecify separate arrays of vertices, normals, and colors and use them to construct a sequence of primitives with a single call to glDrawArrays.

When glDrawArrays is called, it uses count sequential elements from each enabled array to construct a sequence of geometric primitives, beginning with element first. mode specifies what kind of primitives are constructed and how the array elements construct those primitives.

Vertex attributes that are modified by glDrawArrays have an unspecified value after glDrawArrays returns. Attributes that aren't modified remain well defined.

Notes

GL_LINE_STRIP_ADJACENCY, GL_LINES_ADJACENCY, GL_TRIANGLE_STRIP_ADJACENCY and GL_TRIANGLES_ADJACENCY are available only if the GL version is 3.2 or greater.

Errors

GL_INVALID_ENUM is generated if mode is not an accepted value.

GL_INVALID_VALUE is generated if count is negative.

GL_INVALID_OPERATION is generated if a non-zero buffer object name is bound to an enabled array and the buffer object's data store is currently mapped.

GL_INVALID_OPERATION is generated if a geometry shader is active and mode is incompatible with the input primitive type of the geometry shader in the currently installed program object.

Examples

Render a vertex array (not loaded into OpenGL) using texture UV, color, and normal vertex attributes.
glEnableVertexAttribArray(texcoord_attrib_index); // Attribute indexes were received from calls to glGetAttribLocation, or passed into glBindAttribLocation.
glEnableVertexAttribArray(normal_attrib_index);
glEnableVertexAttribArray(color_attrib_index);
glEnableVertexAttribArray(position_attrib_index);

glVertexAttribPointer(texcoord_attrib_index, 2, GL_FLOAT, false, 0, texcoords_data); // texcoords_data is a float*, 2 per vertex, representing UV coordinates.
glVertexAttribPointer(normal_attrib_index, 3, GL_FLOAT, false, 0, normals_data); // normals_data is a float*, 3 per vertex, representing normal vectors.
glVertexAttribPointer(color_attrib_index, 3, GL_UNSIGNED_BYTE, true, sizeof(unsigned char)*3, colors_data); // colors_data is a unsigned char*, 3 per vertex, representing the color of each vertex.
glVertexAttribPointer(position_attrib_index, 3, GL_FLOAT, false, 0, vertex_data); // vertex_data is a float*, 3 per vertex, representing the position of each vertex

glDrawArrays(GL_TRIANGLES, 0, vertex_count); // vertex_count is an integer containing the number of indices to be rendered

glDisableVertexAttribArray(position_attrib_index);
glDisableVertexAttribArray(texcoord_attrib_index);
glDisableVertexAttribArray(normal_attrib_index);
glDisableVertexAttribArray(color_attrib_index);

See Also

glDrawArraysInstanced, glDrawElements, glDrawRangeElements,

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