NAME

SYNOPSIS

DESCRIPTION

This is intended for very specific effects, either by itself or when combined with a vertex shader stage. It is also usable for when you need to show a sparsely populated area efficiently as a point-cloud but without the setup of a 3D pipeline and a rendertarget.

By setting *s* or *t* to 1, tesselation is disabled and the underlying mesh shape is deallocated. Updating the mesh shape to *s* > 1 and *t* > 1 will regenerate and repopulate the individual attributes for vertices and texture coordinates.

By setting the boolean depth argument after the *s* and *t* forms to false, image drawing will not require a depth buffer, avoiding the costly switch between 2D and 3D style processing.

The vertices will be distributed in the -1..1 range (-1,-1 in upper left corner, 1,1 in lower right) while the texture coordinates go in the 0..1 range with 0,0 at the upper left corner.

The storage can be accessed through the optional callback and has the signature of (refobj, n_vertices, vertex_size) where refobj is a userdata table that supports:

:vertices(ind) => x, y, z, w :vertices(ind, x, y, z, w) => nil for fetching and updating, with xyzw matching vertex_size (=2, only xy, =3 only xyz, => w,y,z).

:colors(ind) => r, g, b, a :colors(ind, new_r, new_g, new_b, new_a) for fetching, activating and updating vertex colors.

:texcos(ind, set_ind) => s, t :texcos(ind, set_ind, new_s, new_t) aliased as :texture_coordinates for fetching and updating texture coordinates, set_ind should be 0 or 1 as there are two possible set of texture coordinates per vertex.

:primitive_type(0 or 1) for switching between triangle soup (0) and point-cloud (1) when rendering.

If any of these storage blocks doesn't exist, an attempt to set an index will force it to be allocated.

The plane is indexed, and the individual indices can be manipulated in order to create degenerate triangles that will be discarded. This is useful to 'slice out' parts of the plane. These can be accessed via: :indices(ind) => p1x, p1y, p2x, p2y, p2z, p3x, p3y, p3z :indices(ind, p1x, p1y, p2x, p2y, p2z, p3x, p3y, p3z) For a vertex size of 3. If the vertex size of 2, omitt the z arguments.

NOTES

1

Picking operations like image_hit does not take tesselation into account. This may be subject to change.

2

EXAMPLE

function image_tesselation0()
      local tess = fill_surface(64, 64, 0, 255, 0);
      show_image(tess);
      image_tesselation(tess, 32, 32,
            function(obj, n_v, size)
                  obj:primitive_type(1);
            end
      );
end

SEE ALSO: