As a rough estimate, there are 250 millions individual blades of grass on a football field. Clone the project and open the sample scene in Unity 2019.3.10f1 (or recent), with URP 7.3.1 (or recent) This file contains a shader that outputs the color white, along with some functions we will use throughout this tutorial. Zooming in, we can see some artifacts on the surface of the blades; this is caused by individual blades casting shadows on themselves. Set the Fence game object to be active in the scene; this gives us a surface for the blades to cast shadows onto. The above is a large chunk of code, but all of the work done is similar to what was done for the width and height of the blade. Add a BendGrassWhenEnabled or BendGrassWhenVisible component to a gameobject that should apply the bend effect when positioned over the grass. After the initial three vertices, each additional vertex forms a new triangle with the previous two vertices. We can now pass this through to the VertexOutput function, and then to the geometryOutput structure. Finally, we will multiply out output vertices by the tangentToLocal matrix, correctly aligning them with their input point's normal. Just like we did for the positions of the vertices, we will first calculate the normals in tangent space, and then transform them to local. Open the Main scene, and open the Grass shader in your preferred code editor. This stage comes between vertex and fragment shader (so do tons of other stages, but you get the point). Another advantage is that we would create only as many triangles as we really need, assuming that the underlying topology which we create our grass on is already optimized. We will start by adding a gradient that runs from the top of the blade to the bottom. I'll get back to you as soon as I can! First part is to create the triangles above the surface of the triangles which are currently being rendered. Note that we rescale the sampled value from the texture from a 0...1 range to be in a -1...1 range. Rather than using texture coordinates assigned to the mesh, we will use the input point's position. For surface shaders, Unity has a built-in tessellation implementation. By taking t to a power, its influence on the forward offset will be non-linear, shaping the blade of grass into a curve. The above declares a geometry shader named geo, with two parameters. We need a grass shader in Unity, build using amplify shader or shaderforge for both HDRP and URP pipelines. Here is my code for this gif on Github: https://github.com/IRCSS/Geometry-Grass-Shader. So what is a geometry shader? The grass blades' dimensions right now are fixed at 1 unit wide, 1 unit tall. As a final step to complete this shader, we will add the ability to cast and receive shadows. I already color coded the layers for later sampling in fragment shader (look at Brute force’s blog post for details of implementation or directly in my code in Github). Find this & more VFX Shaders on the Unity Asset Store. At the time I was learning Unreal Engine 4 and custom shaders are primarily made through blueprints. When a mesh is exported from a 3D modelling package, it usually has the binormals (also called the bitangents) already stored in the mesh data. Note the line declaring float3x3 transformMatrix—here we select between our two transformation matrices, taking transformationMatrixFacing for the vertices at the base, and transformationMatrix for all others. Modifying the Tessellation Uniform property will demonstrate the subdivision effect. Instead of importing these binormals, Unity simply grabs each binormal's direction and assigns it to the tangent's w coordinate. I have chosen a more procedural approach because I thought it would be a more challenging and fun way to make grass. After Unity renders a shadow map from the perspective of a shadow casting light, it will run a pass "collecting" the shadows into a screen space texture. Pretty decent for 5 minutes of coding. We also make sure that our SubShader uses the geometry shader, by declaring it inside the Pass. The shader will take an input mesh, and from each vertex on the mesh generate a blade of grass using a geometry shader. Grass Placement. Make sure the grass is billboarded (it will use a default shader otherwise). The idea First of all, I want to show you what was my intents before doing a grass shader for Crumble: I wanted the grass to be fully dynamic, so I actually m You can alternatively message me through Twitter or Reddit. If you like the look of it but can't be bothered to follow the tutorial (I tried it myself and encountered many errors), there is a github repository … I hope this helps! However, sometimes post-processed anti-aliasing is not always appropriate (such as when working with virtual reality); this thread on the Unity forums has a good discussion for alternative solutions to this problem. Toon shading (often called cel shading) is a rendering style designed to make 3D surfaces emulate 2D, flat surfaces.This style entered the mainstream with games like Jet Set Radio and The Wind Waker.. The good thing about the geometry shader is that it creates the extra triangles directly on the GPU memory. We'll make that change now. In simpler terms, we will define the blade in space local to the vertex emitting it, and then transform it to be local to the mesh. Paint Details in the Terrain Inspector Initially, a Terrain has no grass or details available. We will correct this by instead constructing our blades with several triangles and bending them along a curve. You need to: Go to "Project" window and press "Create" new "Material". As well, we will use the built-in shader variable _Time to scroll the wind texture along our grass surface. It is unnecessary to redefine them in our grass shader; they can be removed. Here are a few blogs for further reading if you are interested:The original blog post from Brute force: https://www.bruteforce-games.com/post/grass-shader-devblog-04Another geometry grass shader with a different approach: https://roystan.net/articles/grass-shader.htmlIntro to geometry shaders in case you are unfamiliar with them: https://jayjingyuliu.wordpress.com/2018/01/24/unity3d-intro-to-geometry-shader/And a fun read, though slightly unrelated, placement of grass in the Witness:https://caseymuratori.com/blog_0011, https://github.com/IRCSS/Geometry-Grass-Shader, https://www.bruteforce-games.com/post/grass-shader-devblog-04, https://roystan.net/articles/grass-shader.html, https://jayjingyuliu.wordpress.com/2018/01/24/unity3d-intro-to-geometry-shader/, Journey of Apache Kafka & Zookeeper Administrator ( Part 8 ), Automated Continuous Delivery of Docker images, The Reasons why you Must Use Visual Studio Code, Raspberry Pi 3 — Shell Scripting — Door Monitor (an IoT Device). So make sure the object you are applying the shader is not rotated in unity. So now that this is done, here are some thoughts on the stuff I won’t implement now but are worth noting: As usual thanks for reading. They are just too specific to this project to release ‘out of the box’. Our geometry shader doesn't yet do anything; add the following code inside the geometry shader to emit a triangle. This makes sense; since the geometry shader occurs immediately before vertex processing, it takes over responsibility from the vertex shader to ensure vertices are outputted in clip space. Unity itself comes with a simple tool that allows for the placement of grass using bushes to retain some artistic control. Uses a geometry shader to generate blades of grass. Alternatively alpha blending could be an option depending on the use. Figure 2: Project creation Of course, in order to test out any shader you create, y… This pass will be used by shadow casting lights in the scene to render the grass's depth to their shadow map. We can correct this by applying linear bias, or translating the clip space positions of the vertices slightly away from the screen. We'll create a second pass that will make use of all of the same shaders as our initial pass, with the exception of the fragment shader—we'll define a new one that is populated with a macro that handles the output for us. The cross product returns a vector perpendicular to its two input vectors. To ensure the normal is facing the correct direction, we make use of the optional VFACE parameter we have included in the fragment shader. The grass shader was one of the first things created for this project. We can now visualize the normals in our ForwardBase fragment shader to verify our work. This way, if there are multiple grass meshes in the world, this will create the illusion they are all part of the same wind system. We will also add some simple illumination, received from the main directional light. In addition, we add a final parameter above the function declaration in square brackets: [maxvertexcount(3)]. The triangles now much more closely resemble blades of grass, but—there are far too few of them. Discarding fragments causes aliasing, since MSAA is not applied on them. Instead, we will subdivide the input mesh using tessellation. Finally, in the Unity editor, apply the Wind texture (found at the root of the project) to the Wind Distortion Map slot of our grass material. It is an optional stage in the graphic pipeline, which the programmer may or may not decide to include for the rendering of their objects. This texture will be similar to a normal map, except with only two channels (red and green) instead of three. When Blade Curvature Amount is greater than 1, each vertex will have its tangent Z position offset by the forward amount passed in to the GenerateGrassVertex function. If we are on deferred and are using TXAA we can use a random value between 0 → 1 to check against the noise texture instead of a fixed alpha cut. This is a huge pain, there are different solutions, none is perfect. There simply are not enough vertices in the input mesh to create the appearance of a dense field. Taking in a position, width, and height, it correctly transforms the vertex by the provided matrix, and assigns it a UV coordinate. This tells the GPU that we will emit (but are not required to) at most 3 vertices. Before we do this, it will be useful to move some of our code calculating our grass vertex positions into a function, as we will be using the code several times in and outside our loop. We'll use a #define statement to allow the shader's author to control the number of segments, and calculate the number of outputted vertices from that. This means our geometry shader will need to also run in the shadow pass to ensure the grass blades exist to cast shadows. The setup is cost efficient, convenient for lighting calculations, also it enables for alot of visual fidelity, but it is not truly “volumetric”. Wood texture used on fence model is sourced from CCO Textures. Now days the geometry shaders are overshadowed a bit by compute shaders, since some benchmarkings suggest that the compute shaders are in some cases faster than geometry shaders doing the same job. Materials define how a surface should be rendered, by including references to the Textures it uses, tiling information, Color tints and more. We'll correct this by defining a second transformation matrix that we apply only to the two base vertices. Shaders in Unity can be written in one of three different ways: Surface Shaders. This tutorial will describe step-by-step how to write a toon shader in Unity. Start by selecting the New button in the top right. We will add some properties to control this, as well as some properties to add some random variation. Code placed in this block will be automatically included in any passes in the shader; this will be useful later, as our shader will have multiple passes. We can now construct a matrix to rotate about this vector, and multiply it into our transformationMatrix. We initial define our segment count to be 3, and update our maxvertexcount to calculate the number of vertices based off the segment count. The shader file has two functions included that will help us do this: rand, which generates a random number from a 3-dimensional input, and AngleAxis3x3, which takes an angle (in radians) and returns a matrix rotating that amount around the provided axis. To create variation and add a more natural look, we'll next make every blade of grass face a random direction. Designed with unity 2019.3.10f1 and URP 7.3.1. The grass will be capable of both casting and receiving shadows. In Unity 2018.2 we added the “Vertex Position” input to Shader Graph, allowing you to adjust and animate your meshes. Download the starter project provided above and open it in the Unity editor. After applying linear shadow bias, banding artifacts are removed from the surface of the triangles. Grass Creation. Once you have finished, click the create project button to begin. As a first pass on our solution, we'll calculate the normal assuming no curvature. My favorite way is to place orthogonal quads per batc h es of grass (cross trees), batch them and distribute them smartly.The setup is cost efficient, convenient for lighting calculations, also it enables for alot of visual fidelity, but it is not truly “volumetric”. We use the input position pos as the random seed for our rotation. Right now, the triangles are all being emitted in the same direction, rather than outwards from the surface of the sphere. In order to cast shadows in Unity, a second pass must be added to the shader. Right now, the vertices in our blades of grass do not have any normals assigned. Rendering in Unity uses Meshes, Materials, Shaders and Textures.They have a close relationship. We will implement lighting using the following common, very simple algorithm to calculate diffuse illumination. Send me some feedback about the tutorial in the form below. If we enable the TessellationExample object in the scene, we can see it already has a material applied that implements tessellation. First, we'll need to modify our GenerateGrassVertex function to take in a Y offset we'll call forward. Note that we transform the normal to world space before we output it; Unity surfaces the main directional light's direction to shaders in world space, making this transformation necessary. The newly created geometry can be streamed down the graphic pipeline, or back to the application (CPU) for further processing. In this tutorial, the grass covers a small 10x10 area. We can access a right and up vector by adding some new vertex inputs. Without interaction, graphical effects can feel static or hollow to players. For a more detailed look at implementing custom lighting in shaders, I would recommend taking a look at my toon shader tutorial. We can now add GenerateGrassVertex calls to our loop to add the vertices to the triangle stream. Inside the loop, we add the variable t. This variable will hold a value, from 0...1, representing how far we are along the blade. [/docembed] [expand title="Unity terrain vegetation system"] This is arguably the most accessible method, and does not require any third-party tools. Each blade of grass will be subdivided into a number of segments. If we wished to have multiple triangle strips, we could call the RestartStrip function on the TriangleStream. Our LightMode tag is set to ShadowCaster, instead of ForwardBase—this communicates to Unity that this pass should be used for rendering the object into shadow maps. Triangles are now correctly drawn with their base positioned at their emitting vertex. My favorite way is to place orthogonal quads per batches of grass (cross trees), batch them and distribute them smartly. This function carries the same responsibilities as our the arguments we currently pass in to VertexOutput to generate our blade vertices. We will start by writing a geometry shader to take in a vertex (or point) as input, and output a single triangle to represent a blade of grass. To create our segmented blade of grass, we will use a for loop. However, because our input mesh (in this case, GrassPlane10x10 found in the Mesh folder) has a triangle mesh topology, this would cause a mismatch between the input mesh topology and our requested input primitive. First, we need to include the CustomTessellation.cginc file. Select Glass material and in Inspector, change Render Mode to "Transparent". Instructions. Each iteration of the loop will add two vertices: a left and a right. BendRadius controls the radius of the bending sphere with center being the pivot of the gameobject. These colors are already defined in the shader file as _TopColor and _BottomColor. Save my name, email, and website in this browser for the next time I comment. To make our triangles look more like blades of grass, we'll need to add some color and variety. This way, every blade will get a different rotation, but it will be consistent between frames. Since our geometry shader is written inside CGINCLUDE blocks, it is available for us to use in any passes in the file. With Shader Graph you can, without even writing a single line of code!. We use it above to invert the normal when necessary. A third vector can be calculated by taking the cross product between the other two vectors. Open the Main scene, and open the Grass shader in your preferred code editor. Other than having a new fragment shader, there are a couple key differences in this pass. triStream.Append(GenerateGrassVertex(pos, width, 0, float2(0, 0), transformationMatrixFacing)); Modifying the Tessellation Uniform property now allows us to control the grass density. Like any kind of space, we can define the tangent space of our vertex with three vectors: a right, forward, and up. Each segment will be rectangular in shape, and made up of two triangles, excluding the top segment—this will be a single triangle representing the blade's tip. Geometry shaders take in a single primitive as input, and can generate zero, one, or many primitives. The shader I’ll be showing here is more on the stylized side, and is act… We will just create n number of triangles, displace them in the direction of the triangle normal and append them to the triangle stream. The tangentNormal, defined as directly backwards on the Y axis, is transformed by the same matrix we used to convert our tangent points to local space. These tutorials are made possible, and kept free and open source, by your support. Naïvely, an implementation for interactable grass would contain two components: something in the game world that is capable of passing data into the shader to tell it what part of the grass is being interacted with, and some code in the shader to interpret that data. This file contains a shader that outputs the color white, along with some functions we will use throughout this tutorial. We'll now use this UV to sample our texture, and create a property to control the wind strength.
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