// Render implementation.
// FUTURE: all kinds of possible optimizations that would need to be
// profiled before implementing.
// • group by vao to avoid switching vao's.
// • group by texture to avoid switching textures.
// • use interleaved vertex data.
// • uniform buffers http://www.opengl.org/wiki/Uniform_Buffer_Object.
// • ... lots more possiblities... leave your fav here.
func (gc *opengl) Render(dr Draw) {
d, ok := dr.(*draw)
if !ok || d == nil {
return
}
// switch state only if necessary.
if gc.depthTest != d.depth {
if d.depth {
gl.Enable(gl.DEPTH_TEST)
} else {
gl.Disable(gl.DEPTH_TEST)
}
gc.depthTest = d.depth
}
// switch shaders only if necessary.
if gc.shader != d.shader {
gl.UseProgram(d.shader)
gc.shader = d.shader
}
// Ask the model to bind its provisioned uniforms.
// FUTURE: only need to bind uniforms that have changed.
gc.bindUniforms(d)
// bind the data buffers and render.
gl.BindVertexArray(d.vao)
switch d.mode {
case LINES:
gl.PolygonMode(gl.FRONT_AND_BACK, gl.LINE)
gl.DrawElements(gl.LINES, d.numFaces, gl.UNSIGNED_SHORT, 0)
gl.PolygonMode(gl.FRONT_AND_BACK, gl.FILL)
case POINTS:
gl.Enable(gl.PROGRAM_POINT_SIZE)
gl.DrawArrays(gl.POINTS, 0, d.numVerts)
gl.Disable(gl.PROGRAM_POINT_SIZE)
case TRIANGLES:
if len(d.texs) > 1 && d.texs[0].fn > 0 {
// Multiple textures on one model specify which verticies they apply to.
for _, tex := range d.texs {
// Use the same texture unit and sampler. Just update which
// image is being sampled.
gl.BindTexture(gl.TEXTURE_2D, tex.tid)
// fn is the number of triangles, 3 indicies per triangle.
// f0 is the offset in triangles where each triangle has 3 indicies
// of 2 bytes (uShort) each.
gl.DrawElements(gl.TRIANGLES, tex.fn*3, gl.UNSIGNED_SHORT, int64(3*2*tex.f0))
}
} else {
// Single textures are handled with a standard bindUniforms
gl.DrawElements(gl.TRIANGLES, d.numFaces, gl.UNSIGNED_SHORT, 0)
}
}
}
// Renderer implementation.
func (gc *opengl) Enable(attribute uint32, enabled bool) {
switch attribute {
case CULL, DEPTH:
if enabled {
gl.Enable(attribute)
} else {
gl.Disable(attribute)
}
case BLEND:
if enabled {
gl.Enable(attribute)
// Using non pre-multiplied alpha colour data so...
gl.BlendFunc(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA)
} else {
gl.Disable(attribute)
}
}
}