# glDrawArrays

Definition: | include pGUI.e include opengl.e glDrawArrays(integer mode, first, count)
Description: | render primitives from array data mode: Specifies what kind of primitives to render, must be one of the values in the table below. first: Specifies the starting index in the enabled arrays. count: Specifies the number of indices to be rendered.
pwa/p2js: | Supported.
Notes: | glDrawArrays specifies multiple geometric primitives with very few subroutine calls. Instead of calling a GL procedure to pass each individual vertex attribute, you can use glVertexAttribPointer to 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:
GL_POINTS | Renders one point at a time, eg [1,1, -1,1, 1,-1, -1,-1] renders 4 points.
GL_LINES | Each (non-overlapping) pair of elements defines a line, eg [-1,1, 1,1, 1,1, 1,0, 1,-1, -1,-1] for 3 lines.
GL_LINE_STRIP | Each overlapping pair of elements defines a line, in effect and even length aside the same as GL_LINES but joined-up. eg [-1,1, 1,1, 1,-1, -1,-1] will render 3 lines.
GL_LINE_LOOP | As per GL_LINE_STRIP except the first and last vertex are also connected.
GL_TRIANGLES | Each (non-overlapping) triplet of elements defines a triangle, eg [-1,1, 1,1, 0,0, 0,0, -1,-1, -1,0]; for 2 triangles.
GL_TRIANGLE_STRIP | Each overlapping triplet of elements defines a triangle, with each sharing two points from the previous and next triangle. eg [1,1, 0,1, 1,0, 0,0, 1,-1, 0,-1] for 4 triangles, notionally abc, bcd, cde, and def.
GL_TRIANGLE_FAN | The first point(/index) is shared by all triangles, eg Each overlapping triplet of elements defines a triangle, with each sharing two points from the previous and next triangle, eg [0.0,0.0, 1.0,0.8, -0.5,1.0, -0.8,0.2, -1.0,-1.0, 1.0,-1.0] draws 4 triangles, notionally abc, acd, ade, and aef.
To enable and disable a generic vertex attribute array, call glEnableVertexAttribArray and glDisableVertexAttribArray. If the current program object, as set by glUseProgram(), is invalid, rendering results are undefined. However, no error is generated for this case.
Errors: | GL_INVALID_ENUM is generated if mode is not an accepted value. GL_INVALID_VALUE is generated if count is negative. GL_INVALID_FRAMEBUFFER_OPERATION is generated if the currently bound framebuffer is not framebuffer complete (i.e. the return value from glCheckFramebufferStatus is not GL_FRAMEBUFFER_COMPLETE).
Associated Gets: | glGet with argument GL_SHADER_COMPILER glGetShaderInfoLog with argument shader glGetShaderSource with argument shader glIsShader
See Also: | ?, glDisableVertexAttribArray, W, glEnableVertexAttribArray, glUseProgram, glVertexAttribPointer DEV See Also glCheckFramebufferStatus, //glDisableVertexAttribArray, glDrawElements, //glEnableVertexAttribArray, //glUseProgram, //glVertexAttribPointer