Let's look at the main use cases for those. For buffers, this means you get to point here to the memory backing of the object.
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For textures on iOS, this means you can call some easy-to-use functions to set and retrieve image data. You can also use a private storage mode, which gives the GPU exclusive access to the data. It allows Metal to apply some optimizations that it wouldn't normally have been able to use if the CPU had access to it. But only the GPU can directly fill the contents of the data.
So you can indirectly fill the data from the CPU by using a blitEncoder from a second intermediate resource that uses shared storage. On the voices with dedicated video memory, setting the resource to use private storage allocates it in video memory only, single copy. And on systems with dedicated video memory, Metal may have to create a second mirrored memory backing for efficient access by both processes. So to recap, we reviewed some of the typical uses for each mode.
On macOS you would use the private storage mode for static assets and your render targets.
Your small dynamic buffers could use the shared storage mode. And your larger buffers with small updates would use the managed storage mode. On iOS, your static data and rendering targets can use the private storage mode. And since our devices use unified memory, dynamic data of any size can use the shared storage mode and still get great performance. Next, let's talk about developing shaders for your graphics application and what API's you use to work with shaders.
When it comes to shader compilation in GL, you have to create a shader object, replace the ShaderSource in the object, make just in time compilation, and verify that the compilation succeeded. And while this workflow has its benefits, your application had to pay the performance costs of compiling all your shaders every time. One of the key ways in which Metal achieves its efficiency is by doing work earlier and less frequently. At build time, Xcode will compile all the Metal ShaderSource files into a default Metal library file and place it in your app bundle for retrieval at runtime.
So this removes the need to compile a lot of it at runtime and cuts the compilation time when your application runs in half. All you need to do is create a Metal library from a file bundled with your application and fetch the shader function from it. So it should look reasonably familiar to most GL developers. You can define enums and namespaces.
And like GLSL, there are built-in vector and matrix types, numerous built-in functions and operations come in and use for graphics. And there are classes to operate on textures that specify sampler state. Like Metal, MSL is also unified for graphics and compute.
And finally, since shaders are pre-compiled, Xcode is able to give you errors, warning, and guidance to help you debug at build time. Let's start defining our shaders. These are the prototypes. In GLSL, void main. There's nothing in the shader that specifies the shader stage. It's purely determined by the shader type passed into the glCreateShader call.
In MSL the shader stage is explicitly specified in the shader code. Here the vertex qualifier indicates that it will be executed for each vertex generating perfect examples. In GLSL, every shader entry point has to be called main and accept and return void. In MSL each entry point has a distinct name. At runtime you can query functions by their distinct name from the precompiled Metal library. Then let's talk about inputs. Because each entry point in GLSL is a main function with no argument, all of the inputs are passed as global arguments. This applies to both vertex attributes and uniform variables.
In Metal all the inputs to the shaded stage are arguments to the entry function. We'll look at them in a second. One of the inputs here that we have is a model view projection matrix. And that made shader development error-prone. In MSL the uniform binding indices are explicitly controlled by the developer within the shader, so an application can bind directly to a specific slot.
In the example here, slot number one. The keyword constant here indicates that the intention for the model view projection is to be uniform for all vertices. The other input to the shader is a set of vertex attributes. In GLSL you typically use separate attribute inputs. The main difference here is that MSL uses a structure of your own design. The staging keywords suggest that each invocation of the shader will receive its own arguments. Once you have all the inputs to the shaders set up, you can actually perform all the calculations.
Then for the outputs, in GLSL the output is split between varying attributes like glTexCoord and predefined variables, in this case gl Position. In MSL, the vertex shader output is combined into your own structure. So we've used a vertex and vertex output structure. Let's scroll up in the MSL code to see what they actually look like.test.licitamos.cl/98.php
Bringing OpenGL Apps to Metal
As mentioned previously, GLSL defines the input vertex attributes separately, and Metal allows you to define them within a structure. In MSL there are a few special keywords for vertex shader input. We mark each structure member with an attribute keyword and assign an attribute index to it.
And GLSL predefines special keywords like GL position to indicate which variable contains vertex coordinates that have been transformed with the model view projection matrix. Similarly, for the vertex output, a structure in MSL, the special keyword position signals that the vertex shader output position is stored in that structure member.
But there's a few things you need to remember about them. Vector and matrix types in your buffers are aligned to 16 bytes or 8 bytes for half precision. So they're not necessarily packed, for example, a float3 has a size of 12 bytes but is aligned to 16 bytes.
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There are specific backed formats you can use if you need them. But you will need to unpack them in the shader before using them. And to make this transition smooth and easy, my colleague Max will show you a really cool tool to help you breeze through it. Thank you. Good evening. Metal, it's not just an API and a shading language, it is also a powerful collection of tools. My name is Max, and I'm going to minimize your hassle porting to Metal. Let's take a look at this scene. It's drawing a model of a temple and a tree, both illuminated by a global light source. Let's port the fragment shader together.
Based on this, I've already created my input structure, as well as my function prototype. Let's begin. So what we are going to do is just copy and paste the contents of the main function directly into our Metal function.
Getting Started - OpenGL Wiki
And here we see the very first powerful thing about Metal. Because the shader's precompiled, we are getting errors instantly. Let's take a closer look. Of course, the building vector types have different names now.
So vec2 becomes a float2; the vec3 becomes the float3; and the vec4 becomes a float4. So we quickly fix that. The next error we are going to see is that like all of our input structures -- all of our global variables are now coming from our input structure.
And because I just used a similar naming scheme, this is also very easy.
And, of course, we have to do the exact same thing for our uniforms. The next error is a little bit more complex. Sampling in Metal is different, so let's take a look. We are going to start from scratch. So we directly can call a sample function on our colorMap. And here we can see how powerful it is to have full auto completion.
So this function expects us to put in a sampler and a texture coordinate. We already have the texture coordinate. We could pass in the sampler as an argument to our function or, conveniently in Metal, we can just declare one in code like this. We need to do the exact same thing for our normalMap.
The last error that we are seeing is that we are writing into, like, one of many OpenGL magic variables. Instead, we are just going to return our final computed color. We can also see that all the other functions, like normalize, dot product, and my favorite function max, are still exactly the same.