src/scene.c

/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 * Copyright 2023 Mike Becker. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   1. Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 *
 *   2. Redistributions in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in the
 *      documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include "ascension/scene.h"
#include "ascension/error.h"

#include "ascension/context.h"

#include <cx/linked_list.h>
#include <cx/array_list.h>
#include <cx/tree.h>
#include <cx/utils.h>

#include "ascension/shader.h"
#include <GL/glew.h>

#include <assert.h>

static CxTreeIterator asc_scene_node_iterator(
        AscSceneNode *node,
        bool visit_on_exit
) {
    return cx_tree_iterator(
            node, visit_on_exit,
            offsetof(AscSceneNode, children),
            offsetof(AscSceneNode, next)
    );
}

static CxTreeVisitor asc_scene_node_visitor(AscSceneNode *node) {
    return cx_tree_visitor(node,
            offsetof(AscSceneNode, children),
            offsetof(AscSceneNode, next)
    );
}

struct asc_render_group_entry {
    asc_scene_draw_func draw;
    AscSceneNode const *node;
};

#define asc_draw_render_group(iter) \
    cx_foreach(struct asc_render_group_entry*, entry, iter) { \
        entry->draw(entry->node); \
    }

void asc_scene_draw(AscSceneNode *root, asc_recti viewport, AscCamera *camera) {
    // create render groups
    CxList *render_group[ASC_RENDER_GROUP_COUNT];
    cx_for_n(i, ASC_RENDER_GROUP_COUNT) {
        render_group[i] = cxArrayListCreateSimple(
                sizeof(struct asc_render_group_entry), 32);
    }

    // skip the root node deliberately, we know it's just the container
    CxTreeVisitor iter = asc_scene_node_visitor(root);
    cxIteratorNext(iter);

    // update the children and add them to the render groups
    cx_foreach(AscSceneNode*, node, iter) {
        node->depth = iter.depth;

        // execute behaviors, first
        if (node->behaviors != NULL) {
            CxIterator behavior_iter = cxListIterator(node->behaviors);
            cx_foreach(asc_scene_update_func, behavior, behavior_iter) {
                behavior(node);
            }
        }

        // TODO: implement culling
        // TODO: implement a hidden flag (requires UCX tree-continue function)

        // check if geometry needs update
        if (node->need_graphics_update) {
            assert(node->update_func != NULL);
            node->need_graphics_update = false;
            node->update_func(node);
        }
        if (node->need_transform_update) {
            node->need_transform_update = false;
            asc_transform_from_parts(
                    node->transform,
                    node->position,
                    node->scale,
                    node->rotation
            );
            asc_mat4f_mulst(
                    node->world_transform,
                    node->transform,
                    node->parent->world_transform
            );
        }

        // add to render group
        if (node->draw_func != NULL) {
            struct asc_render_group_entry entry = {
                    node->draw_func, node
            };
            cxListAdd(render_group[node->render_group], &entry);
        }
    }

    // set the viewport (in OpenGL we need to invert the Y axis)
    glViewport(
            viewport.pos.x,
            -viewport.pos.y,
            viewport.size.width,
            viewport.size.height
    );

    // -------------------------
    // process the render groups
    // -------------------------
    AscShaderProgram *shader;
    CxIterator render_iter;

    // 2D Elements
    // ===========
    glEnable(GL_DEPTH_TEST);
    glClear(GL_DEPTH_BUFFER_BIT);

    // Sprites
    // -------
    // TODO: implement view matrix for 2D worlds
    shader = &asc_context.active_window->glctx.shader.sprite.base;
    glUseProgram(shader->id);
    glUniformMatrix4fv(shader->projection, 1,
                       GL_FALSE, camera->projection);

    // render opaque sprites from front to back
    glDisable(GL_BLEND);
    render_iter = cxListBackwardsIterator(render_group[ASC_RENDER_GROUP_SPRITE_OPAQUE]);
    asc_draw_render_group(render_iter);

    // render sprites with alpha value from back to front
    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    render_iter = cxListIterator(render_group[ASC_RENDER_GROUP_SPRITE_BLEND]);
    asc_draw_render_group(render_iter);

    // destroy render groups
    cx_for_n(i, ASC_RENDER_GROUP_COUNT) {
        cxListDestroy(render_group[i]);
    }
}

AscSceneNode *asc_scene_node_empty(void) {
    AscSceneNode *node = calloc(1, sizeof(AscSceneNode));
    node->free_func = (asc_scene_free_func) free;
    asc_transform_identity(node->transform);
    asc_transform_identity(node->world_transform);
    return node;
}

void asc_scene_node_free(AscSceneNode *node) {
    if (node == NULL) return;

    // remove this node from its parent
    asc_scene_node_unlink(node);

    // free the entire subtree
    CxTreeIterator iter = asc_scene_node_iterator(node, true);
    cx_foreach(AscSceneNode*, child, iter) {
        if (!iter.exiting) continue;
        if (child->behaviors != NULL) {
            cxListDestroy(child->behaviors);
        }
        if (child->free_func != NULL) {
            child->free_func(child);
        } else {
            free(child);
        }
    }
}

void asc_scene_node_link(AscSceneNode * restrict parent, AscSceneNode * restrict node) {
    cx_tree_link(
            parent, node,
            offsetof(AscSceneNode, parent),
            offsetof(AscSceneNode, children),
            offsetof(AscSceneNode, prev),
            offsetof(AscSceneNode, next)
    );
}

void asc_scene_node_unlink(AscSceneNode *node) {
    cx_tree_unlink(
            node,
            offsetof(AscSceneNode, parent),
            offsetof(AscSceneNode, children),
            offsetof(AscSceneNode, prev),
            offsetof(AscSceneNode, next)
    );
}

void asc_scene_add_behavior(
        AscSceneNode *node,
        asc_scene_update_func behavior
) {
    if (node->behaviors == NULL) {
        node->behaviors = cxLinkedListCreateSimple(CX_STORE_POINTERS);
    }
    cxListAdd(node->behaviors, behavior);
}

void asc_scene_remove_behavior(
        AscSceneNode *node,
        asc_scene_update_func behavior
) {
    if (node->behaviors != NULL) {
        cxListFindRemove(node->behaviors, behavior);
    }
}

void asc_update_transform(AscSceneNode *node) {
    if (node->need_transform_update) return;

    CxTreeIterator iter = asc_scene_node_iterator(node, false);
    cx_foreach(AscSceneNode*, n, iter) {
        // TODO: break/continue when subtree is already marked for update
        n->need_transform_update = true;
    }
}