In OpenGL ES this is implemented in EXT_multi_draw_arrays extension, if
it is not available, the functionality is emulated using sequence of
normal draw() calls.
Functionality provided by GL 3.3 and ARB_instanced_arrays, on ES2 this
is again implemented in three different extensions --
{ANGLE,EXT,NV}_instanced_arrays. They are disabled until Magnum has
proper extension loading on ES.
On desktop GL this is provided by ARB_draw_instanced (GL 3.1). Base
instance is available only on desktop GL (4.2, ARB_base_instance). In
ES2 the instanced functionality is provided by three (!) different
extensions (ANGLE_instanced_arrays, EXT_draw_instanced,
NV_draw_instanced), the proper implementation is chosen on context
creation based on what extension is available. Though we don't have
extension loader for ES yet, thus all these extensions are disabled and
the implementation has assertion in it.
Added blind test which tests only that something has been drawn and no
errors were emitted, but not whether the right command is used. I'll
probably need to check this later, because the Mesh::draw() behemoth is
going slightly out of hand :)
The well-known issue is that gl*DrawElements*BaseVertex() is not
supported in OpenGL ES. It is possible to work around it by
reconfiguring whole VAO, but that seems to be a bit overkill. Currently
the draw() function just asserts that base vertex is not specified for
indexed meshes.
Previously the API didn't encourage the user to set up and activate
shader before drawing the meshes, leading to unintuitive behavior:
// Can I just call draw() or do I have to fully understand the
// meaning of the universe before?
mesh.draw();
Now the draw() needs the shader passed explicitly as parameter, which
should hint that the shader must be set up somehow:
// Right, so this needs just a shader and that's all. Expecting this
// I fortunately *did* configure all the uniforms before this call.
mesh.draw(shader);
It is also possible to pass the shader as rvalue, in case the drawing is
just a one-off thing and is already fully configured.
mesh.draw(MyShader{});
As usual, the original API is kept, is marked as deprecated and will be
removed in some future release.
Each texture has slightly different usage requirements and having
everything under one generic class is not worth the additional runtime
checks and whatnot. The current way with Texture::Target enum
(hopefully not too widely used) is now deprecated and will be removed in
some future release. However general Texture1D/2D/3D usage is not
changed in any way.
Vladimír Vondruš