examples/model/skybox/example/skybox.render_script

-- Copyright 2020-2025 The Defold Foundation
-- Copyright 2014-2020 King
-- Copyright 2009-2014 Ragnar Svensson, Christian Murray
-- Licensed under the Defold License version 1.0 (the "License"); you may not use
-- this file except in compliance with the License.
--
-- You may obtain a copy of the License, together with FAQs at
-- https://www.defold.com/license
--
-- Unless required by applicable law or agreed to in writing, software distributed
-- under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
-- CONDITIONS OF ANY KIND, either express or implied. See the License for the
-- specific language governing permissions and limitations under the License.

--
-- message constants
--
local MSG_CLEAR_COLOR =         hash("clear_color")
local MSG_WINDOW_RESIZED =      hash("window_resized")
local MSG_SET_VIEW_PROJ =       hash("set_view_projection")
local MSG_SET_CAMERA_PROJ =     hash("use_camera_projection")
local MSG_USE_STRETCH_PROJ =    hash("use_stretch_projection")
local MSG_USE_FIXED_PROJ =      hash("use_fixed_projection")
local MSG_USE_FIXED_FIT_PROJ =  hash("use_fixed_fit_projection")

local DEFAULT_NEAR = -1
local DEFAULT_FAR =   1
local DEFAULT_ZOOM =  1

--
-- projection that centers content with maintained aspect ratio and optional zoom
--
local function get_fixed_projection(camera, state)
    camera.zoom = camera.zoom or DEFAULT_ZOOM
    local projected_width = state.window_width / camera.zoom
    local projected_height = state.window_height / camera.zoom
    local left = -(projected_width - state.width) / 2
    local bottom = -(projected_height - state.height) / 2
    local right = left + projected_width
    local top = bottom + projected_height
    return vmath.matrix4_orthographic(left, right, bottom, top, camera.near, camera.far)
end
--
-- projection that centers and fits content with maintained aspect ratio
--
local function get_fixed_fit_projection(camera, state)
    camera.zoom = math.min(state.window_width / state.width, state.window_height / state.height)
    return get_fixed_projection(camera, state)
end
--
-- projection that stretches content
--
local function get_stretch_projection(camera, state)
    return vmath.matrix4_orthographic(0, state.width, 0, state.height, camera.near, camera.far)
end
--
-- projection for gui
--
local function get_gui_projection(camera, state)
    return vmath.matrix4_orthographic(0, state.window_width, 0, state.window_height, camera.near, camera.far)
end

local function update_clear_color(state, color)
    if color then
        state.clear_buffers[graphics.BUFFER_TYPE_COLOR0_BIT] = color
    end
end

local function update_camera(camera, state)
    if camera.projection_fn then
        camera.proj = camera.projection_fn(camera, state)
        camera.options.frustum = camera.proj * camera.view
    end
end

local function update_state(state)
    state.window_width = render.get_window_width()
    state.window_height = render.get_window_height()
    state.valid = state.window_width > 0 and state.window_height > 0
    if not state.valid then
        return false
    end
    -- Make sure state updated only once when resize window
    if state.window_width == state.prev_window_width and state.window_height == state.prev_window_height then
        return true
    end
    state.prev_window_width = state.window_width
    state.prev_window_height = state.window_height
    state.width = render.get_width()
    state.height = render.get_height()
    for _, camera in pairs(state.cameras) do
        update_camera(camera, state)
    end
    return true
end

local function init_camera(camera, projection_fn, near, far, zoom)
    camera.view = vmath.matrix4()
    camera.near = near == nil and DEFAULT_NEAR or near
    camera.far = far == nil and DEFAULT_FAR or far
    camera.zoom = zoom == nil and DEFAULT_ZOOM or zoom
    camera.projection_fn = projection_fn
end

local function create_predicates(...)
    local arg = {...}
    local predicates = {}
    for _, predicate_name in pairs(arg) do
        predicates[predicate_name] = render.predicate({predicate_name})
    end
    return predicates
end

local function create_camera(state, name, is_main_camera)
    local camera = {}
    camera.options = {}
    state.cameras[name] = camera
    if is_main_camera then
        state.main_camera = camera
    end
    return camera
end

local function create_state()
    local state = {}
    local color = vmath.vector4(0, 0, 0, 0)
    color.x = sys.get_config_number("render.clear_color_red", 0)
    color.y = sys.get_config_number("render.clear_color_green", 0)
    color.z = sys.get_config_number("render.clear_color_blue", 0)
    color.w = sys.get_config_number("render.clear_color_alpha", 0)
    state.clear_buffers = {
        [graphics.BUFFER_TYPE_COLOR0_BIT] = color,
        [graphics.BUFFER_TYPE_DEPTH_BIT] = 1,
        [graphics.BUFFER_TYPE_STENCIL_BIT] = 0
    }
    state.cameras = {}
    return state
end

local function set_camera_world(state)
    local camera_components = camera.get_cameras()

    -- This will set the last enabled camera from the stack of camera components
    if #camera_components > 0 then
        for i = #camera_components, 1, -1 do
            if camera.get_enabled(camera_components[i]) then
                local camera_component = state.cameras.camera_component
                camera_component.camera = camera_components[i]
                render.set_camera(camera_component.camera, { use_frustum = true })
                -- The frustum will be overridden by the render.set_camera call,
                -- so we don't need to return anything here other than an empty table.
                return camera_component.options
            end
        end
    end

    -- If no active camera was found, we use the default main "camera world" camera
    local camera_world = state.cameras.camera_world
    render.set_view(camera_world.view)
    render.set_projection(camera_world.proj)
    return camera_world.options
end

local function reset_camera_world(state)
    -- unbind the camera if a camera component is used
    if state.cameras.camera_component.camera then
        state.cameras.camera_component.camera = nil
        render.set_camera()
    end
end

function init(self)
    self.predicates = create_predicates("tile", "gui", "particle", "model", "skybox", "debug_text")

    -- default is stretch projection. copy from builtins and change for different projection
    -- or send a message to the render script to change projection:
    -- msg.post("@render:", "use_stretch_projection", { near = -1, far = 1 })
    -- msg.post("@render:", "use_fixed_projection", { near = -1, far = 1, zoom = 2 })
    -- msg.post("@render:", "use_fixed_fit_projection", { near = -1, far = 1 })

    local state = create_state()
    self.state = state

    local camera_world = create_camera(state, "camera_world", true)
    init_camera(camera_world, get_stretch_projection)
    local camera_gui = create_camera(state, "camera_gui")
    init_camera(camera_gui, get_gui_projection)
    -- Create a special camera that wraps camera components (if they exist)
    -- It will take precedence over any other camera, and not change from messages
    local camera_component = create_camera(state, "camera_component")
    update_state(state)
end

function update(self)
    local state = self.state
    if not state.valid then
        if not update_state(state) then
            return
        end
    end

    local predicates = self.predicates
    -- clear screen buffers
    --
    -- turn on depth_mask before `render.clear()` to clear it as well
    render.set_depth_mask(true)
    render.set_stencil_mask(0xff)
    render.clear(state.clear_buffers)

    -- setup camera view and projection
    --
    local draw_options_world = set_camera_world(state)
    render.set_viewport(0, 0, state.window_width, state.window_height)

    -- set states used for all the world predicates
    render.set_blend_func(graphics.BLEND_FACTOR_SRC_ALPHA, graphics.BLEND_FACTOR_ONE_MINUS_SRC_ALPHA)
    render.enable_state(graphics.STATE_DEPTH_TEST)


    -- render `model` predicate for default 3D material
    --
    render.enable_state(graphics.STATE_CULL_FACE)
    render.draw(predicates.model, draw_options_world)
    render.set_depth_mask(false)
    render.disable_state(graphics.STATE_CULL_FACE)

    
    -- render `skybox`
    -- https://www.ogldev.org/www/tutorial25/tutorial25.html
    --
    render.enable_state(graphics.STATE_CULL_FACE)
    -- Usually we want to cull the triangles that are facing away from the camera
    -- However in the case of a skybox the camera is placed inside of a box/sphere
    -- so we want to see their front, rather than their back
    render.set_cull_face(graphics.FACE_TYPE_FRONT)
    -- By default, we tell OpenGL that an incoming fragment wins the depth test if
    -- its Z value is less than the stored one. However, in the case of a skybox
    -- the Z value is always the far Z. The far Z is clipped when the depth test
    -- function is set to "less than". To make it part of the scene we change the
    -- depth function to "less than or equal".
    render.set_depth_func(graphics.COMPARE_FUNC_LEQUAL)
    render.draw(predicates.skybox, draw_options_world)
    render.set_depth_mask(false)
    render.set_depth_func(graphics.COMPARE_FUNC_LESS)
    render.set_cull_face(graphics.FACE_TYPE_BACK)
    render.disable_state(graphics.STATE_CULL_FACE)

    -- render the other components: sprites, tilemaps, particles etc
    --
    render.enable_state(graphics.STATE_BLEND)
    render.draw(predicates.tile, draw_options_world)
    render.draw(predicates.particle, draw_options_world)
    render.disable_state(graphics.STATE_DEPTH_TEST)

    render.draw_debug3d()

    reset_camera_world(state)

    -- render GUI
    --
    local camera_gui = state.cameras.camera_gui
    render.set_view(camera_gui.view)
    render.set_projection(camera_gui.proj)

    render.enable_state(graphics.STATE_STENCIL_TEST)
    render.draw(predicates.gui, camera_gui.options)
    render.draw(predicates.debug_text, camera_gui.options)
    render.disable_state(graphics.STATE_STENCIL_TEST)
    render.disable_state(graphics.STATE_BLEND)
end

function on_message(self, message_id, message)
    local state = self.state
    local camera = state.main_camera

    if message_id == MSG_CLEAR_COLOR then
        update_clear_color(state, message.color)
    elseif message_id == MSG_WINDOW_RESIZED then
        update_state(state)
    elseif message_id == MSG_SET_VIEW_PROJ then
        camera.view = message.view
        self.camera_projection = message.projection or vmath.matrix4()
        update_camera(camera, state)
    elseif message_id == MSG_SET_CAMERA_PROJ then
        camera.projection_fn = function() return self.camera_projection end
    elseif message_id == MSG_USE_STRETCH_PROJ then
        init_camera(camera, get_stretch_projection, message.near, message.far)
        update_camera(camera, state)
    elseif message_id == MSG_USE_FIXED_PROJ then
        init_camera(camera, get_fixed_projection, message.near, message.far, message.zoom)
        update_camera(camera, state)
    elseif message_id == MSG_USE_FIXED_FIT_PROJ then
        init_camera(camera, get_fixed_fit_projection, message.near, message.far)
        update_camera(camera, state)
    end
end