src/mesh.c

/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 * Copyright 2025 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/error.h"
#include "ascension/mesh.h"

#include <cx/allocator.h>

#include <GL/glew.h>

int asc_mesh_allocate_buffers(AscMesh *mesh, unsigned count) {
    asc_dprintf("Allocate mesh buffers for %u meshes.", count);
    GLuint buffers[count];
    GLuint arrays[count];
    glGenBuffers(count, buffers);
    glGenVertexArrays(count, arrays);
    for (unsigned i = 0; i < count; i++) {
        mesh[i].vbo = buffers[i];
        mesh[i].vao = arrays[i];
    }
    return asc_error_catch_gl("Allocating mesh buffers");
}

void asc_mesh_free_buffers(AscMesh *mesh, unsigned count) {
    if (count == 1 && mesh->vbo == 0) return; // hack to skip this function until we remove it
    asc_dprintf("Free mesh buffers for %u meshes.", count);
    GLuint buffers[count];
    GLuint arrays[count];

    for (unsigned i = 0; i < count; i++) {
        buffers[i] = mesh[i].vbo;
        arrays[i] = mesh[i].vao;
        mesh[i].vbo = 0;
        mesh[i].vao = 0;
    }

    asc_error_catch_gl("OpenGL has unchecked error flags before deleting mesh buffers");
    glDeleteBuffers(count, buffers);
    glDeleteVertexArrays(count, arrays);
    asc_error_catch_gl("Deleting mesh buffers");
}

void asc_mesh_draw_triangle_strip(const AscMesh *mesh) {
    glBindVertexArray(mesh->vao);
    glDrawArrays(GL_TRIANGLE_STRIP, 0, mesh->vtx_count);
    asc_error_catch_gl("Drawing mesh");
#ifndef NDEBUG
    // only unbind in debug mode to detect accidental re-use of the wrong VAO
    glBindVertexArray(0);
#endif
}

void asc_mesh_destroy(AscMesh *mesh) {
    asc_mesh_free_buffers(mesh, 1);
    cxFreeDefault(mesh->vtx_data);
}

void asc_mesh_init_plane_2d(AscMesh *mesh, struct asc_mesh_init_plane_2d_args args) {
    if (mesh->vao == 0) {
        if (asc_mesh_allocate_buffers(mesh, 1)) return;
        // bind the buffer and configure the vertex attributes
        glBindBuffer(GL_ARRAY_BUFFER, mesh->vbo);
        glBindVertexArray(mesh->vao);
        glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(asc_vertex2d), (void*)offsetof(asc_vertex2d, pos));
        glEnableVertexAttribArray(0);
        glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, sizeof(asc_vertex2d), (void*)offsetof(asc_vertex2d, uv));
        glEnableVertexAttribArray(1);
    } else {
        // only bind the buffer for updating the data
        glBindBuffer(GL_ARRAY_BUFFER, mesh->vbo);
    }
    if (asc_error_catch_gl("Binding VBO or VAO")) return;

    unsigned required_memory = 4 * sizeof(asc_vertex2d);

    // free any previous data
    if (mesh->vtx_data && mesh->vtx_data_size < required_memory) {
        cxFreeDefault(mesh->vtx_data);
        mesh->vtx_data = NULL;
    }

    // allocate memory
    asc_vertex2d *data;
    if (mesh->vtx_data == NULL) {
        asc_dprintf("Create plane in VBO %u and VAO %u", mesh->vbo, mesh->vao);
        mesh->vtx_data_size = required_memory;
        data = cxMallocDefault(mesh->vtx_data_size);
        mesh->vtx_data = (float*) data;
    } else {
        data = (asc_vertex2d*) mesh->vtx_data;
    }
    mesh->vtx_count = 4;

    // default values
    args.size.x = ASC_NONZERO_OR(1.f, args.size.x);
    args.size.y = ASC_NONZERO_OR(1.f, args.size.y);
    args.uv_scale.x = ASC_NONZERO_OR(1.f, args.uv_scale.x);
    args.uv_scale.y = ASC_NONZERO_OR(1.f, args.uv_scale.y);

    // bottom left
    data[0].pos = ASC_VEC2F(0.0f, 0.0f);
    data[0].uv = ASC_VEC2F(args.uv_offset.x, args.uv_offset.y);
    // top left
    data[1].pos = ASC_VEC2F(0.0f, args.size.y);
    data[1].uv = ASC_VEC2F(args.uv_offset.x, args.uv_offset.y + args.uv_scale.y);
    // bottom right
    data[2].pos = ASC_VEC2F(args.size.x, 0.0f);
    data[2].uv = ASC_VEC2F(args.uv_offset.x + args.uv_scale.x, args.uv_offset.y);
    // top right
    data[3].pos = ASC_VEC2F(args.size.x, args.size.y);
    data[3].uv = ASC_VEC2F(args.uv_offset.x + args.uv_scale.x, args.uv_offset.y + args.uv_scale.y);
    glBufferData(GL_ARRAY_BUFFER, mesh->vtx_data_size, mesh->vtx_data, GL_STATIC_DRAW);
    asc_error_catch_gl("Writing VBO data");
}