DrawArrays

DrawArrays is a rendering command used in OpenGL and its derivatives to render primitives directly from per-vertex attribute arrays without using an index buffer. In OpenGL, the function glDrawArrays takes three parameters: mode, first, and count. The mode selects the primitive type (for example GL_POINTS, GL_LINES, GL_LINE_STRIP, GL_LINE_LOOP, GL_TRIANGLES, GL_TRIANGLE_STRIP, GL_TRIANGLE_FAN). The vertex data consumed are the ones described by the current vertex array state, typically configured via Vertex Buffer Objects and a Vertex Array Object. The parameters specify that vertices with indices in the range [first, first + count) are read in order and assembled into primitives.

DrawArrays uses non-indexed data; if you need to reuse vertices across primitives, a indexed drawing approach with glDrawElements is used instead. For advanced rendering, there is also an instanced variant, glDrawArraysInstanced, which draws multiple instances of a set of vertices in a single call.

Typical usage involves creating and binding a VAO, uploading vertex data to VBOs, configuring vertex attribute pointers, and then issuing glDrawArrays with the desired mode and counts. The count value must reflect the number of vertices, not the number of primitives, and the first value must be a valid offset within the bound data. Misconfiguration of vertex attributes or bound buffers can cause GL errors or incomplete rendering.

In WebGL, the corresponding function is gl.drawArrays(mode, first, count) and follows similar semantics, adapted to the WebGL API. See also glDrawElements and glDrawArraysInstanced for related indexed and instanced rendering.