以OpenGL/ES视角介绍gfx-hal(Vulkan) Texture接口使用

文档列表见： Rust 移动端跨平台复杂图形渲染项目开发系列总结（目录）

就OpenGL、OpenGL ES、gfx-hal(1:1仿Vulkan接口定义)等KHR定义的图形库接口而言，Texture都有创建、上传数据、下载绘制结果数据、作为Framebuffer的挂载点等操作，下面分别介绍。

OpenGL(ES)的Texture对应到Vulkan分别是Image、ImageView、Memory、Sampler，上传/下载Image的数据还需要配合Buffer，涉及到非常多细节。如果是刚开始学习图形开发，不建议使用Vulkan。

创建纹理的整体流程：

1. 创建Image
2. 创建Image关联的Memory
3. 关联Image到Memory

上传数据到纹理的整体流程：

1. 创建Staging Buffer
2. 创建Fence
3. 创建用于数据拷贝的Submmit
   • 创建Command Buffer
   • 创建Barrier
   • 向Command Buffer提交Barrier
   • 向Command Buffer提交Copy Buffer to Image命令
   • 结束Command Buffer编码
4. 提交Submmit到GPU命令队列

在Shader使用纹理的整体流程：

1. 创建ImageView
2. 创建Sampler
3. 创建、配置DescriptorSet、DescriptorSetLayout

下载绘制结果数据的整体流程：

待续

作为Framebuffer挂载点的整体流程：

待续

创建纹理的整体流程

创建Image

let kind = image::Kind::D2(dims.width as image::Size, dims.height as image::Size, 1 /* Layer */, 1 /* NumSamples */);
let unbound = device.create_image(
        kind,
        1 /* mip_levels */,
        ColorFormat::SELF,
        image::Tiling::Optimal,
        image::Usage::TRANSFER_DST | image::Usage::SAMPLED,
        image::StorageFlags::empty(),
    )
    .unwrap();
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创建Image关联的Memory

let req = device.get_image_requirements(&unbound);

let device_type = adapter
    .memory_types
    .iter()
    .enumerate()
    .position(|(id, memory_type)| {
        req.type_mask & (1 << id) != 0 && memory_type.properties.contains(memory::Properties::DEVICE_LOCAL)
    })
    .unwrap()
    .into();

let memory = device.allocate_memory(device_type, req.size).unwrap();
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关联Image到Memory

let image = device.bind_image_memory(&memory, 0, unbound).unwrap();
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上传数据到纹理的整体流程

创建传输Fence

let mut transfered_image_fence = device.create_fence(false);
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上传CPU数据到纹理

// copy buffer to texture
{
    let submit = {
        let mut cmd_buffer = staging_pool.acquire_command_buffer(false);

        let image_barrier = memory::Barrier::Image {
            states: (image::Access::empty(), image::Layout::Undefined)
                ..(image::Access::TRANSFER_WRITE, image::Layout::TransferDstOptimal),
            target: &image,
            range: COLOR_RANGE.clone(),
        };

        cmd_buffer.pipeline_barrier(
            PipelineStage::TOP_OF_PIPE..PipelineStage::TRANSFER,
            memory::Dependencies::empty(),
            &[image_barrier],
        );

        cmd_buffer.copy_buffer_to_image(
            buffer.as_ref().unwrap().get_buffer(),
            &image,
            image::Layout::TransferDstOptimal,
            &[command::BufferImageCopy {
                buffer_offset: 0,
                buffer_width: row_pitch / (stride as u32),
                buffer_height: dims.height as u32,
                image_layers: image::SubresourceLayers {
                    aspects: f::Aspects::COLOR,
                    level: 0,
                    layers: 0..1,
                },
                image_offset: image::Offset { x: 0, y: 0, z: 0 },
                image_extent: image::Extent {
                    width: dims.width,
                    height: dims.height,
                    depth: 1,
                },
            }],
        );

        let image_barrier = memory::Barrier::Image {
            states: (image::Access::TRANSFER_WRITE, image::Layout::TransferDstOptimal)
                ..(image::Access::SHADER_READ, image::Layout::ShaderReadOnlyOptimal),
            target: &image,
            range: COLOR_RANGE.clone(),
        };
        cmd_buffer.pipeline_barrier(
            PipelineStage::TRANSFER..PipelineStage::FRAGMENT_SHADER,
            memory::Dependencies::empty(),
            &[image_barrier],
        );

        cmd_buffer.finish()
    };

    let submission = Submission::new().submit(Some(submit));
    device_state.queues.queues[0].submit(submission, Some(&mut transfered_image_fence));
}
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在Shader使用纹理的整体流程

创建ImageView

let image_view = device.create_image_view(
        &image,
        image::ViewKind::D2,
        ColorFormat::SELF,
        Swizzle::NO,
        COLOR_RANGE.clone(),
    )
    .unwrap();
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创建Sampler

let sampler = device.create_sampler(image::SamplerInfo::new(image::Filter::Linear, image::WrapMode::Clamp));
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配置DescriptorSet

device.write_descriptor_sets(vec![
    pso::DescriptorSetWrite {
        set: &desc_set,
        binding: 0,
        array_offset: 0,
        descriptors: Some(pso::Descriptor::Image(&image_srv, image::Layout::Undefined)),
    },
    pso::DescriptorSetWrite {
        set: &desc_set,
        binding: 1,
        array_offset: 0,
        descriptors: Some(pso::Descriptor::Sampler(&sampler)),
    },
]);
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