WebGLRenderingContext: drawElements() method

{{APIRef("WebGL")}}{{AvailableInWorkers}}

The WebGLRenderingContext.drawElements() method of the WebGL API renders primitives from array data.

Syntax

drawElements(mode, count, type, offset)

Parameters

• mode

  • : A {{domxref("WebGL_API/Types", "GLenum")}} specifying the type primitive to render. Possible values are:
    • gl.POINTS: Draws a single dot.
    • gl.LINE_STRIP: Draws a straight line to the next vertex.
    • gl.LINE_LOOP: Draws a straight line to the next vertex, and connects the last vertex back to the first.
    • gl.LINES: Draws a line between a pair of vertices.
    • gl.TRIANGLE_STRIP
    • gl.TRIANGLE_FAN
    • gl.TRIANGLES: Draws a triangle for a group of three vertices.

• count

  • : A {{domxref("WebGL_API/Types", "GLsizei")}} specifying the number of elements of the bound element array buffer to be rendered. For example, to draw a wireframe triangle with gl.LINES the count should be 2 endpoints per line × 3 lines = 6 elements. However to draw the same wireframe triangle with gl.LINE_STRIP the element array buffer does not repeat the indices for the end of the first line/start of the second line, and end of the second line/start of the third line, so count will be four. To draw the same triangle with gl.LINE_LOOP the element array buffer does not repeat the first/last vertex either so count will be three.

• type

  • : A {{domxref("WebGL_API/Types", "GLenum")}} specifying the type of the values in the element array buffer. Possible values are:

    • gl.UNSIGNED_BYTE
    • gl.UNSIGNED_SHORT

    When using the {{domxref("OES_element_index_uint")}} extension:

    • gl.UNSIGNED_INT

• offset

  • : A {{domxref("WebGL_API/Types", "GLintptr")}} specifying a byte offset in the element array buffer. Must be a valid multiple of the size of the given type.

Return value

None ({{jsxref("undefined")}}).

Exceptions

• If mode is not one of the accepted values, a gl.INVALID_ENUM error is thrown.
• If offset is not a valid multiple of the size of the given type, a gl.INVALID_OPERATION error is thrown.
• If count is negative, a gl.INVALID_VALUE error is thrown.

Examples

gl.drawElements(gl.POINTS, 8, gl.UNSIGNED_BYTE, 0);

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• {{domxref("WebGLRenderingContext.drawArrays()")}}
• {{domxref("OES_element_index_uint")}}
• {{domxref("WEBGL_multi_draw.multiDrawElementsWEBGL()")}}