1.164 class sdl_mesh

An sdl_mesh holds triangles that the SDL renderer draws without Cairo, using SDL_RenderGeometry(). An sdl_layer shows it if it is the sdl_layer<-mesh of the layer. Each corner (vertex) of a triangle has a position, a colour and a position in the texture of the layer. The colours are interpolated over the triangle and multiplied by the texture. Without a texture, the triangle shows the colours only.

Positions are in the coordinates of the window and mapped through sdl_layer<-transform, so a whole mesh can be moved, rotated and scaled. Positions in the texture are in its pixels. The layer's sdl_mesh<-alpha, sdl_mesh<-tint, sdl_mesh<-blend and sdl_mesh<-scale_mode apply; its sdl_mesh<-area, sdl_mesh<-scale, sdl_mesh<-source, sdl_mesh<-angle, sdl_mesh<-flip, sdl_mesh<-offset and sdl_mesh<-slices are ignored.

Meshes are good for:

• Shapes with gradients, e.g., coloured plots.
• Warping a texture, e.g., a camera image on a deformed grid.
• Many particles in a single layer: one textured rectangle (two triangles) per particle, rebuilt on every frame. This is much cheaper than an sdl_layer per particle.

Small meshes can be built using sdl_mesh->append and sdl_mesh->triangle. For large meshes that change on every frame, use the predicate pce_sdl_mesh_set/3, which replaces all vertices and triangles in one call:

pce_sdl_mesh_set(+Mesh, +Vertices, +Indices)

Vertices is a list of v(X,Y), v(X,Y,U,V) or v(X,Y,U,V,rgba(R,G,B,A)), where U,V is the position in the texture and R, G, B and A are integers 0..255. The default colour is opaque white. Indices is a list of indices of Vertices, three per triangle, counting from 0. If Indices is [], each three consecutive vertices make a triangle. For example, a rectangle with a red and a blue side:

new(M, sdl_mesh),
pce_sdl_mesh_set(M,
                 [ v(0,0,0,0,rgba(255,0,0,255)),
                   v(100,0,0,0,rgba(0,0,255,255)),
                   v(100,50,0,0,rgba(0,0,255,255)),
                   v(0,50,0,0,rgba(255,0,0,255))
                 ],
                 [0,1,2, 0,2,3]),
new(L, sdl_layer),
send(L, mesh, M),
send(Window, append, L).

The edges of the triangles are not anti-aliased. frame<-image draws meshes with Cairo; a textured triangle whose corners have different colours is drawn using their average colour.

See also

- class sdl_layer
- class sdl_texture

1.164.1 Instance variables

sdl_mesh <- layers: chain

The sdl_layer objects that show the mesh. Changing the mesh shows their windows again.

1.164.2 Send methods

sdl_mesh ->initialise:

Create an empty mesh.

sdl_mesh ->append: position=point, texture=[point], colour=[colour]

Append a vertex at position, in the coordinates of the window. texture is its position in the texture, in pixels (default point(0,0)), and colour its colour (default opaque white). The index of the new vertex is the old sdl_mesh<-count.

sdl_mesh ->triangle: int, int, int

Append a triangle between the vertices with these indices. Raises an error if there is no such vertex. If a mesh has no triangles, each three consecutive vertices make a triangle.

sdl_mesh ->clear:

Remove all vertices and triangles.

sdl_mesh ->changed:

Show the windows of the layers again. This is done by the methods that change the mesh.

1.164.3 Get methods

sdl_mesh <-count: -> int

Number of vertices.