a_buffer.cxx

#include "a_buffer.h"
 
namespace cgv {
    namespace render {
 
        void a_buffer::ensure_buffers(context& ctx)
        {
            unsigned num_pixels = ctx.get_width() * ctx.get_height();
            // Generate buffers for the a-buffer transparency implementation
            node_counter_buffer.create_or_resize(ctx, sizeof(GLuint));
            head_pointer_buffer.create_or_resize(ctx, num_pixels * sizeof(GLuint));
            node_buffer.create_or_resize(ctx, nodes_per_pixel * 3 * num_pixels * sizeof(GLuint));
        }
        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);
            options.define_macro_if_not_default("PRE_MULTIPLY_OPACITY", pre_multiply_opacity, true);
            options.define_macro_if_not_default("Z_FIGHT_REMOVAL", z_fight_removal, 0);
            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;
 
            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);
            node_counter_buffer.destruct(ctx);
            head_pointer_buffer.destruct(ctx);
            node_buffer.destruct(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);
 
            if (!depth_tex.is_created())
                depth_tex.create(ctx, TT_2D, ctx.get_width(), ctx.get_height());
 
            ensure_buffers(ctx);
 
            // Clear the atomic counter
            const GLuint zero = 0;
            node_counter_buffer.replace(ctx, 0, &zero, 1);
 
            // Clear the head pointer buffer using a compute shader
            head_pointer_buffer.bind(ctx, 0);
            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);
            head_pointer_buffer.unbind(ctx, 0);
 
            // Check if the shader program needs to be rebuilt
            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
            node_counter_buffer.bind(ctx, node_counter_binding_point);
            head_pointer_buffer.bind(ctx, head_pointers_binding_point);
            node_buffer.bind(ctx, nodes_binding_point);
 
            return true;
        }
        // return current number of nodes in node buffer
        void a_buffer::disable(context& ctx, size_t* node_count)
        {
            // Unbind texture and buffers
            depth_tex.disable(ctx);
 
            node_counter_buffer.unbind(ctx, node_counter_binding_point);
            head_pointer_buffer.unbind(ctx, head_pointers_binding_point);
            node_buffer.unbind(ctx, nodes_binding_point);
 
            // Read back node count if requested
            if(node_count) {
                GLuint temp = 0;
                node_counter_buffer.copy(ctx, 0, &temp, 1);
                *node_count = temp;
            }
        }
        void a_buffer::finish_frame(context& ctx)
        {
            ctx.push_blend_state();
            ctx.enable_blending();
            ctx.set_blend_func_back_to_front();
 
            head_pointer_buffer.bind(ctx, 0);
            node_buffer.bind(ctx, 1);
 
            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);
            if (z_fight_removal > 0) {
                a_buffer_prog.set_uniform(ctx, "z_fight_delta", pow(10.0f, z_fight_removal_exp));
                if (z_fight_removal > 1)
                    a_buffer_prog.set_uniform(ctx, "z_fight_window_width", z_fight_window_width);
            }
            glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
            a_buffer_prog.disable(ctx);
 
            head_pointer_buffer.unbind(ctx, 0);
            node_buffer.unbind(ctx, 1);
 
            ctx.pop_blend_state();
        }
    }
}