This tutorial will describe step-by-step how to write a grass shader for Unity. First, we need to include the CustomTessellation.cginc file. Each iteration of the loop will add two vertices: a left and a right. 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. Rather than using texture coordinates assigned to the mesh, we will use the input point's position. This way, every blade will get a different rotation, but it will be consistent between frames. This ensures that the shader compiles all necessary variants required for shadow casting. To create variation and add a more natural look, we'll next make every blade of grass face a random direction. To create interest and realism, the blades will have randomized dimensions and rotations, and be affected by wind. Use the following syntax to declare a geometry-shader object. Great tutorial but I am wondering (and didn't find a proper … Wood texture used on fence model is sourced from CCO Textures. In this tutorial, the grass covers a small 10x10 area. Geometry shaders wo r k by procedurally generating vertices on the GPU side before sending them to the fragment shader to fill in. The cross product returns a vector perpendicular to its two input vectors. As we move up the blade, the height increases, and the width decreases (as it tapers inwards). Note that the vertex shader vert in CustomTessellation.cginc simply passes the input directly through to the tessellation stage; the job of creating the vertexOutput struct is taken care of by the tessVert function, called inside the domain shader. What makes the geometry shader interesting is that it is able to convert the original primitive (set of vertices) to completely different primitives, possibly … This is an example that shows how to implement a geometry shader that is compatible with the standard lighting model in Unity. Before sampling the wind texture, we will need to construct a UV coordinate. View all posts by jingyuLiu. The subdivided blade of grass represented as a triangle strip, constructed one vertex at a time. I know I'm looking at making a Geometry shader, but can't find any documentation or examples of geometry addition shaders that play well with Unity - most only modify existing vertices in the vertex subshader. triStream.Append(GenerateGrassVertex(pos, width, 0, float2(0, 0), transformationMatrixFacing)); We will correct this by instead constructing our blades with several triangles and bending them along a curve. Active 1 year, 10 months ago. This could be adapted to work with grass; instead of drawing ripples where the character is, the blades of grass could be rotated downward to simulate the footstep impacts. This file is adapted from this article by Catlike Coding, which is an excellent reference on how to implement tessellation in Unity. These tutorials are made possible, and kept free and open source, by your support. Create a free website or blog at WordPress.com. Note that the return type of this function is void, so that we need another way to pass our modified data to the next stage. unitycoder / wireframe.shader. Before we begin outputting more vertices from our geometry shader, we will need to increase the maxvertexcount. If we retrieve the source for this macro from Autolight.cginc, we can see it requires the shadow coordinate to have a specific name. We will use these two channels as the X and Y directions of the wind. To create interest and realism, the blades will have randomized dimensions and rotations, and be affected by wind. ( Log Out /  Can cast and receive shadows. 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. Our geometry shader doesn't yet do anything; add the following code inside the geometry shader to emit a triangle. Skip to content. This tutorial will describe step-by-step how to write a grass shader for Unity. Embed. As this tutorial is already very long, I abstained from including a section about how to have objects in the world interact with and influence the grass. World of Zero (Tutorial by World of Zero) where he codes a geometry shader for a point cloud grass generator. 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. 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. Note that we rescale the sampled value from the texture from a 0...1 range to be in a -1...1 range. 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. We'll now use this UV to sample our texture, and create a property to control the wind strength. Finally, we need to ensure our shader is correctly configured to receive shadows. So as we know, we used to use a struct called v2f to carry data we need from vertex to fragment shader. The rand function returns a number in the 0...1 range; we will multiply this by two Pi to get the full gamut of angular values. The first, triangle float4 IN[3], states that we will take in a single triangle (composed of three points) as our input. 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. Geometry shaders take in a single primitive as input, and can generate zero, one, or many primitives. This has yielded some odd results. In addition, we add a final parameter above the function declaration in square brackets: [maxvertexcount(3)]. Download shader: We will use a Unity macro for this, and include it in an #if statement to ensure the operation is only run during the shadow pass. b) This method accepts an input of type v2g, regards it as a triangle (since we know that models are made of triangle primitives), and names it as input whose [] operator would give access to the three vertices of the triangle. When a geometry shader is active, it is invoked once for every primitive passed down or generated earlier in the pipeline. While we could emit a blade from all three input points, this would cause neighbouring triangles to redundantly emit blades atop one another. Right now, the vertices in our blades of grass do not have any normals assigned. Lower values of _BladeForward and _BladeCurve will result in a more organized, well tended field of grass, while larger values will have the opposite effect. If we enable the TessellationExample object in the scene, we can see it already has a material applied that implements tessellation. Als Shader in der klassischen Grafikpipeline wird der Geometry-Shader nach dem Vertex-Shader aufgerufen. With all three vectors, we can construct a matrix to transform between tangent and local space. 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. I've found that a value of 5 produces good results. Zooming in, we can see some artifacts on the surface of the blades; this is caused by individual blades casting shadows on themselves. ( Log Out /  After the initial three vertices, each additional vertex forms a new triangle with the previous two vertices. The issue here is that we initially defined our "up" direction to be on the Y axis; in tangent space, however, convention usually dictates the up direction be along the Z axis. Geometry shaders are an optional part of the rendering pipeline. Their main purpose is to get the information from the separate vertices via the vertex shader, assemble the primitives that will form the object (usually it’s going to be triangles) and send the final … creative coder. Unity 2018.3 project source for completed Grass Shader Tutorial from the site roystan.net. If we wished to have multiple triangle strips, we could call the RestartStrip function on the TriangleStream. A geometry-shader object processes entire primitives. With these vectors, we can construct a matrix to rotate our blade of grass from tangent to local space. Unity is the ultimate game development platform. 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. If you open CustomTessellation.cginc, you will note that it has already defined vertexInput and vertexOutput structs, as well as a vertex shader. This function carries the same responsibilities as our the arguments we currently pass in to VertexOutput to generate our blade vertices. Alternatively, this could be resolved by using meshes with the Points topology type as the input mesh for our geometry shader. Because our shader has Cull set to Off, both sides of the blade of grass are rendered. Each blade of grass will be subdivided into a number of segments. We first need to find the direction by which we extrude the point A. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. How can I create a shader that "cuts" through all geometry, only rendering the clearing background in Unity? This looks closer to what we want, but is not entirely correct. Geometry shader, in ShaderLab term, is actually a method in Unity shader program. Therefore, when the anti-aliased scene samples the non-anti-aliased shadow map, artifacts occur. Its job is to subdivide a a single input surface into a many primitives. Grass Geometry Shader for Unity. We will multiply each vertex in our blade of grass by this matrix before it is passed into UnityObjectToClipPos, which expects a vertex in local space. A macro we use below, SHADOW_ATTENUATION, is no different. So as we process each triangle, we need to first find the longer side of the triangle and consider this as the central side because in this way we can extrude our pyramid tip from the middle point of this lateral side: Now we just need to construct three triangles, namely ABC, ACD, and ABD. Each … Controls the density of the blades by tessellating the input mesh. In the ForwardBase pass's fragment shader, we can use a macro to retrieve a float value representing whether the surface is in shadows or not. The geometry shader sees two triangles, each with three vertices. The surface of the prism is just rendering the skybox of the scene (a starry sky). To control the density of the grass, tessellation will be used to subdivide the input mesh. The outputs of the vertex shader (or Tessellation Stage, as appropriate) are thus fed to the GS as arrays of variables. We'll modify our code to reflect this. Thanks for reading. ...where N is the normal of the surface, L is the normalized direction of the main directional light, and I is the calculated illumination. We can now add the hull and domain shaders to our grass shader. We apply the _WindDistortionMap scale and offset to our position, and then further offset it by _Time.y, scaled by _WindFrequency. Unity官方文档关于Geometry Shader的内容较少。. The heart of a surface shader is its surface function. Without interaction, graphical effects can feel static or hollow to players. If the grass isn't animating in the Scene view, click the Toggle skybox, fog, and various other effects button to enable animated materials. We can now visualize the normals in our ForwardBase fragment shader to verify our work. As we want our grass to be generated correctly for all kinds of surfaces, it is important to test it on different shaped meshes. The blade's base is no longer pinned to the ground; it is intersecting the ground (in. The UV coordinates of the three vertices of our grass blades. 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. Each individual variable will be an array of the length of the primitive's vertex count; for interface blocks, the block itself will be a… Note that matrix multiplication is not commutative; the order of the operands does matter. From far away, this looks correct—however, if we inspect the blades of grass up close, we'll notice that the entire blade is rotating, causing the base to no longer be pinned to the ground. c) TriangleStream is a little bit tricky. The rotation can be applied to the blade by multiplying it with the existing tangentToLocal matrix. With our function working correctly, we are ready to move our vertex generation code into a for loop. Once again, we apply this matrix through rotation, taking care to add it in the correct order. After we finish one point, we append it to the triangleStream. Other entries in the Create > Shader menu create barebone shaders or other types, for example a basic surface shader. This may be desirable for well tended grass, like on a putting green, but does not accurately represent grass in the wild. You'll notice that these functions, along with the vertex shader, are enclosed in a CGINCLUDE block placed outside the SubShader. After every triangle finishes, we call tristream.RestartStrip(); to indicate that we now start a new triangle. Join the Official Oculus Discussion Forums and talk about Oculus Rift, Oculus Touch, Samsung Gear VR, and virtual reality. Even when multisample anti-aliasing (MSAA) is enabled, Unity does not apply anti-aliasing to the scene's depth texture, which is used when constructing the screen-space shadow map. We'll correct this by defining a second transformation matrix that we apply only to the two base vertices. We can access a right and up vector by adding some new vertex inputs. ). We can now construct a matrix to rotate about this vector, and multiply it into our transformationMatrix. 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. 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. Writing geometry shaders is hard Implementing a geometry shader in Unity is not easy as it seems because surface shaders don't allow geometry stage customization -- This means that you have to implement the whole … Uses a geometry shader to generate blades of grass. I am a game design and cs student at NYU. There simply are not enough vertices in the input mesh to create the appearance of a dense field. Share Copy sharable link … The geometry shader can then transform these vertices as it sees fit before sending them to the next shader stage. 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. One solution is to use anti-aliasing applied during post processing, which is available in Unity's post processing package. To do this, we will add a preprocessor directive to the ForwardBase pass to compile all necessary shader variants. An example of how to do this with water can be found here. This means our geometry shader will need to also run in the shadow pass to ensure the grass blades exist to cast shadows.