a_buffer.cxx

#include "a_buffer.h"
 
namespace cgv {
    namespace render {
 
        void a_buffer::ensure_buffer(GLuint& buffer, GLenum target, GLsizeiptr size, const void* data, GLenum usage)
        {
            if (buffer == 0) {
                glGenBuffers(1, &buffer);
                glBindBuffer(target, buffer);
                glBufferData(target, size, data, usage);
                glBindBuffer(target, 0);
            }
        }
 
        void a_buffer::destruct_buffer(GLuint& buffer)
        {
            if (buffer != 0) {
                glDeleteBuffers(1, &buffer);
                buffer = 0;
            }
        }
        void a_buffer::destruct_buffers(context& ctx)
        {
            destruct_buffer(node_buffer_counter);
            destruct_buffer(head_pointer_buffer);
            destruct_buffer(node_buffer);
        }
        void a_buffer::ensure_buffers(context& ctx)
        {
            unsigned num_pixels = ctx.get_width() * ctx.get_height();
            // Generate buffers for the a-buffer transparency implementation
            ensure_buffer(node_buffer_counter, GL_ATOMIC_COUNTER_BUFFER, sizeof(GLuint), NULL, GL_STATIC_DRAW); // atomic counter variable
            ensure_buffer(head_pointer_buffer, GL_SHADER_STORAGE_BUFFER, num_pixels * sizeof(GLuint), NULL); // linked list head pointer buffer
            if (node_buffer != 0 && last_nodes_per_pixel != nodes_per_pixel)
                destruct_buffer(node_buffer);
            ensure_buffer(node_buffer, GL_SHADER_STORAGE_BUFFER, nodes_per_pixel * 3 * num_pixels * sizeof(GLuint), NULL); // buffer to store linked list nodes, each with 3 32-bit values; reserve space for as much as 64 fragments per pixel
            last_nodes_per_pixel = nodes_per_pixel;
        }
        void a_buffer::update_shader_program_options(shader_compile_options& options, bool include_binding_points)
        {
            options.define_macro_if_not_default("MAX_FRAGMENTS", fragments_per_pixel, 32u);
            if(include_binding_points) {
                options.define_macro_if_not_default("NODE_COUNTER_BINDING_POINT", node_counter_binding_point, 0);
                options.define_macro_if_not_default("HEAD_POINTERS_BINDING_POINT", head_pointers_binding_point, 0);
                options.define_macro_if_not_default("NODES_BINDING_POINT", nodes_binding_point, 1);
            }
        }
        void a_buffer::update_shader_program_options(shader_compile_options& options)
        {
            update_shader_program_options(options, true);
        }
        a_buffer::a_buffer(unsigned _fragments_per_pixel, unsigned _nodes_per_pixel, int _depth_tex_unit, 
            int _node_counter_binding_point, int _head_pointers_binding_point, int _nodes_binding_point)
            : depth_tex("[D]")
        {
            depth_tex.set_min_filter(TF_NEAREST);
            depth_tex.set_mag_filter(TF_NEAREST);
            fragments_per_pixel = _fragments_per_pixel;
            nodes_per_pixel = _nodes_per_pixel;
            last_nodes_per_pixel = 0;
            node_buffer_counter = 0;
            head_pointer_buffer = 0;
            node_buffer = 0;
 
            depth_tex_unit = _depth_tex_unit;
            node_counter_binding_point = _node_counter_binding_point;
            head_pointers_binding_point = _head_pointers_binding_point;
            nodes_binding_point = _nodes_binding_point;
 
            init_frame_called = false;
        }
        bool a_buffer::init(context& ctx)
        {
            if (!clear_ssbo_prog.build_files(ctx, "a_buffer_clear", true))
                return false;
            update_shader_program_options(prog_options, false);
            if (!a_buffer_prog.build_program(ctx, "a_buffer.glpr", prog_options, true))
                return false;
            last_prog_options = prog_options;
            return true;
        }
        void a_buffer::destruct(context& ctx)
        {
            clear_ssbo_prog.destruct(ctx);
            a_buffer_prog.destruct(ctx);
            depth_tex.destruct(ctx);
            destruct_buffers(ctx);
        }
        void a_buffer::init_frame(context& ctx)
        {
            // Ensure depth texture and node buffers of correct size
            if (depth_tex.is_created() && (ctx.get_width() != depth_tex.get_width() || ctx.get_height() != depth_tex.get_height())) {
                depth_tex.destruct(ctx);
                destruct_buffer(head_pointer_buffer);
                destruct_buffer(node_buffer);
            }
            if (!depth_tex.is_created())
                depth_tex.create(ctx, TT_2D, ctx.get_width(), ctx.get_height());
            ensure_buffers(ctx);
 
            // Clear the atomic counter
            glBindBuffer(GL_ATOMIC_COUNTER_BUFFER, node_buffer_counter);
            GLuint* ptr = (GLuint*)glMapBufferRange(GL_ATOMIC_COUNTER_BUFFER, 0, sizeof(GLuint), GL_MAP_WRITE_BIT | GL_MAP_INVALIDATE_BUFFER_BIT | GL_MAP_UNSYNCHRONIZED_BIT);
            memset(ptr, 0, sizeof(GLuint));
            glUnmapBuffer(GL_ATOMIC_COUNTER_BUFFER);
            glBindBuffer(GL_ATOMIC_COUNTER_BUFFER, 0);
 
            // Clear the head pointer buffer
            glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, head_pointer_buffer);
            unsigned buffer_size = ctx.get_width() * ctx.get_height();
            clear_ssbo_prog.enable(ctx);
            clear_ssbo_prog.set_uniform(ctx, "size", buffer_size);
            clear_ssbo_prog.set_uniform(ctx, "clear_value", -1);
            glDispatchCompute(GLuint(ceil(buffer_size / 4)), 1, 1);
            glMemoryBarrier(GL_SHADER_STORAGE_BARRIER_BIT);
            clear_ssbo_prog.disable(ctx);
            glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, 0);
 
            // check for rebuild of program
            update_shader_program_options(prog_options, false);
            if (prog_options != last_prog_options) {
                if (a_buffer_prog.is_created())
                    a_buffer_prog.destruct(ctx);
                if (a_buffer_prog.build_program(ctx, "a_buffer.glpr", prog_options, true)) {
                    last_prog_options = prog_options;
                    std::cout << "a_buffer: rebuilt shader program" << std::endl;
                }
            }
            init_frame_called = true;
        }
        bool a_buffer::enable(context& ctx, shader_program& prog, int tex_unit)
        {
            // in first call after init_frame, copy depth buffer to depth texture
            if (init_frame_called) {
                depth_tex.replace_from_buffer(ctx, 0, 0, 0, 0, ctx.get_width(), ctx.get_height());
                init_frame_called = false;
            }
            // set program uniforms
            if (!prog.set_uniform(ctx, "viewport_dims", ivec2(ctx.get_width(), ctx.get_height()))) {
                std::cerr << "ERROR in a_buffer::enable(): uniform ivec2 viewport_dims not found in program." << std::endl;
                return false;
            }
            if (!prog.set_uniform(ctx, "nodes_per_pixel", (int)nodes_per_pixel)) {
                std::cerr << "ERROR in a_buffer::enable(): uniform int nodes_per_pixel not found in program." << std::endl;
                return false;
            }
            // enable depth texture
            if (tex_unit == -1)
                tex_unit = depth_tex_unit;
            depth_tex.enable(ctx, tex_unit);
            if (!prog.set_uniform(ctx, "depth_tex", tex_unit)) {
                std::cerr << "ERROR in a_buffer::enable(): uniform sampler2D depth_tex not found in program." << std::endl;
                return false;
            }
            // Bind buffers for first a-buffer pass         
            glBindBufferBase(GL_ATOMIC_COUNTER_BUFFER, node_counter_binding_point, node_buffer_counter);
            glBindBufferBase(GL_SHADER_STORAGE_BUFFER, head_pointers_binding_point, head_pointer_buffer);
            glBindBufferBase(GL_SHADER_STORAGE_BUFFER, nodes_binding_point, node_buffer);
            return true;
        }
        // return current number of nodes in node buffer
        size_t a_buffer::disable(context& ctx)
        {
            // Unbind texture and buffers
            depth_tex.disable(ctx);
            glBindBufferBase(GL_ATOMIC_COUNTER_BUFFER, node_counter_binding_point, 0);
            glBindBufferBase(GL_SHADER_STORAGE_BUFFER, head_pointers_binding_point, 0);
            glBindBufferBase(GL_SHADER_STORAGE_BUFFER, nodes_binding_point, 0);
 
            // Clear atomic counter, read it back and use it as return value
            glBindBuffer(GL_ATOMIC_COUNTER_BUFFER, node_buffer_counter);
            GLuint* ptr = (GLuint*)glMapBufferRange(GL_ATOMIC_COUNTER_BUFFER, 0, sizeof(GLuint), GL_MAP_READ_BIT);
            GLuint node_cnt = *ptr;
            glUnmapBuffer(GL_ATOMIC_COUNTER_BUFFER);
            glBindBuffer(GL_ATOMIC_COUNTER_BUFFER, 0);
            return node_cnt;
        }
        void a_buffer::finish_frame(context& ctx)
        {
            glEnable(GL_BLEND);
            glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
 
            glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, head_pointer_buffer);
            glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 1, node_buffer);
 
            a_buffer_prog.enable(ctx);
            a_buffer_prog.set_uniform(ctx, "viewport_dims", ivec2(ctx.get_width(), ctx.get_height()));
            a_buffer_prog.set_uniform(ctx, "nodes_per_pixel", nodes_per_pixel);
            glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
            a_buffer_prog.disable(ctx);
 
            glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, 0);
            glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 1, 0);
 
            glDisable(GL_BLEND);
        }
    }
}