Method prepare_instance_data

samples/api/instancing/instancing.cpp:362–426

}

void Instancing::prepare_instance_data()
{
	std::vector<InstanceData> instance_data;
	instance_data.resize(INSTANCE_COUNT);

	std::default_random_engine              rnd_generator(lock_simulation_speed ? 0 : static_cast<unsigned>(time(nullptr)));
	std::uniform_real_distribution<float>   uniform_dist(0.0, 1.0);
	std::uniform_int_distribution<uint32_t> rnd_texture_index(0, textures.rocks.image->get_vk_image().get_array_layer_count());

	// Distribute rocks randomly on two different rings
	for (auto i = 0; i < INSTANCE_COUNT / 2; i++)
	{
		glm::vec2 ring0{7.0f, 11.0f};
		glm::vec2 ring1{14.0f, 18.0f};

		float rho, theta;

		// Inner ring
		rho                       = sqrt((pow(ring0[1], 2.0f) - pow(ring0[0], 2.0f)) * uniform_dist(rnd_generator) + pow(ring0[0], 2.0f));
		theta                     = 2.0f * glm::pi<float>() * uniform_dist(rnd_generator);
		instance_data[i].pos      = glm::vec3(rho * cos(theta), uniform_dist(rnd_generator) * 0.5f - 0.25f, rho * sin(theta));
		instance_data[i].rot      = glm::vec3(glm::pi<float>() * uniform_dist(rnd_generator), glm::pi<float>() * uniform_dist(rnd_generator), glm::pi<float>() * uniform_dist(rnd_generator));
		instance_data[i].scale    = 1.5f + uniform_dist(rnd_generator) - uniform_dist(rnd_generator);
		instance_data[i].texIndex = rnd_texture_index(rnd_generator);
		instance_data[i].scale *= 0.75f;

		// Outer ring
		rho                                                                 = sqrt((pow(ring1[1], 2.0f) - pow(ring1[0], 2.0f)) * uniform_dist(rnd_generator) + pow(ring1[0], 2.0f));
		theta                                                               = 2.0f * glm::pi<float>() * uniform_dist(rnd_generator);
		instance_data[static_cast<size_t>(i + INSTANCE_COUNT / 2)].pos      = glm::vec3(rho * cos(theta), uniform_dist(rnd_generator) * 0.5f - 0.25f, rho * sin(theta));
		instance_data[static_cast<size_t>(i + INSTANCE_COUNT / 2)].rot      = glm::vec3(glm::pi<float>() * uniform_dist(rnd_generator), glm::pi<float>() * uniform_dist(rnd_generator), glm::pi<float>() * uniform_dist(rnd_generator));
		instance_data[static_cast<size_t>(i + INSTANCE_COUNT / 2)].scale    = 1.5f + uniform_dist(rnd_generator) - uniform_dist(rnd_generator);
		instance_data[static_cast<size_t>(i + INSTANCE_COUNT / 2)].texIndex = rnd_texture_index(rnd_generator);
		instance_data[static_cast<size_t>(i + INSTANCE_COUNT / 2)].scale *= 0.75f;
	}

	instance_buffer.size = instance_data.size() * sizeof(InstanceData);

	// Staging
	// Instanced data is static, copy to device local memory
	// On devices with separate memory types for host visible and device local memory this will result in better performance
	// On devices with unified memory types (DEVICE_LOCAL_BIT and HOST_VISIBLE_BIT supported at once) this isn't necessary and you could skip the staging

	vkb::core::BufferC staging_buffer = vkb::core::BufferC::create_staging_buffer(get_device(), instance_data);

	instance_buffer.buffer = std::make_unique<vkb::core::BufferC>(get_device(), instance_buffer.size, VK_BUFFER_USAGE_VERTEX_BUFFER_BIT | VK_BUFFER_USAGE_TRANSFER_DST_BIT, VMA_MEMORY_USAGE_GPU_ONLY);

	// Copy to staging buffer
	VkCommandBuffer copy_command = get_device().create_command_buffer(VK_COMMAND_BUFFER_LEVEL_PRIMARY, true);

	VkBufferCopy copy_region = {};
	copy_region.size         = instance_buffer.size;
	vkCmdCopyBuffer(
	    copy_command,
	    staging_buffer.get_handle(),
	    instance_buffer.buffer->get_handle(),
	    1,
	    &copy_region);