Fur Shader GRAPHICS PROGRAMMING 2

Transcription

1 Fur Shader GRAPHICS PROGRAMMING 2 2DAE5 - GAMEDEVELEPMENT Academiejaar :

2 Inhoudsopgave Introduction... 2 Shells... 2 Fins... 2 The process... 2 The shader... 3 General... 3 Matrices... 3 Light... 3 Textures... 4 Fur variables... 5 Forces... 5 States... 7 Structs... 7 Pass 1: Drawing base mesh... 8 Vertex shader... 8 Pixel Shader... 8 Pass 2: Generate and drawing the fins... 9 Vertex shader... 9 Geometry shader... 9 Pixel shader Pass 3: Generate and drawing the shells Vertex shader Geometry shader Pixel shader Final result Conclusion Future improvements References

3 Introduction In this paper I will explain the process of creating a fur shader. I wrote this shader in HLSL using shader model 4_0 and DirectX10. A common technique to make real time fur is using shells and fins. We texture the shells that are extruded from the mesh. To make the fur more realistic I generate extra fins, extruded from the mesh. Shells How do I create this shells? The shells are layers that are extruded from the mesh. Each time I extrude the vertices of the mesh along their normal. I use a dotted shell opacity texture to create them, this will create the illusion that the hairs are coming out of the mesh. Each shell is then textured using the color of a diffuse texture. Fins How do I create this fins? I first have to calculate where we want them. I create a fin at the edges of our model. Then I create a quad in the geometry shader and texture it. The process 2

4 For my shader, I use 3 passes: 1. Draw the mesh 2. Generate and draw the fins 3. Draw the shells The shader General Matrices Light 3

5 Textures Diffuse texture: In this texture we put a texture of a patern (example: a tiger). Diffuse color: We select a color from the colorwheel. Shell opacity texture: In this texture we put a random noise texture saved as a PNG. Fin opacity texture: In this texture we put a sideview of hair (black/white), saved as a PNG. Bool texture diffuse: To check if I use a texture or a simple diffuse color. Diffuse scale: To set the scale of the diffuse texture. Opacity scale: To set the scale of the opacity texture. 4

6 Fur variables Fur length: Slider where you can change the length of the fur. Layers: Slider where you can change the amount of layers of the fur. Density: Slider where you can change the density of the fur. Fin offset: Slider where you can change the offset of the fins. Forces Gravity: The force in the negative y direction. Gravity intensity: Slider where you can change the intensity of the gravity. 5

7 Force 1: The force in the negative x direction. Force 1 intensity: Slider where you can change the intensity of force one. Force 2: The force in the negative z direction. Force 2 intensity: Slider where you can change the intensity of force two. 6

8 States BackfaceCulling: Only draw front side of the quads. NoneCulling: Draw both sides of the quads. EnableBlending: Enables alpha/opacity blending. m_texturesampler: Samples colors from the textures. Use lineair filtering for minification, magnification and mipmapping. Wrap: extends the texture function by repeating the image at every junction. DepthState: Disable writing depth info but enables reading depth. Structs VS_DATA: Is the input for the vertex shader and the geometry shader. It has a position, normal and texcoord. GS_DATA: Is the input for the pixel shader. It has a psoiton, normal, texcoord and an integer for the amount of layers. 7

9 Pass 1: Drawing base mesh Pass 1 is a simple pass. In this pass we draw the mesh itself. This is the base form from which we extrude the hairs. Vertex shader The vertex shader for the first pass is very basic. Here I set the input in world space using the matrices. I also assign the texcoord and return the values. Pixel Shader The pixel shader is basic. I create a diffusecolor. Then I calculate the shadow using the dotproduct of the negatif normal and the lightdirection. I saturate the shadow so it is a value between [0,1]. Then I multiply the shadow with the sampled color from the texture. In the end I darken the values. Finally I return the diffusecolor. 8

10 Pass 2: Generate and drawing the fins In pass2 I generate and draw the fins. The fins are projected on quads, which are perpendicular to the mesh surface. First I change the rasterizerstate to noneculling, which means that the fins are visable on both sides of the quads. In this pass we use a custom DepthStencilState. This state prevents writing depth information. But it can read depth information so that fins don t show through the mesh or through object that are in front of it. Vertex shader In this vertex shader I pass the data on to the geometry shader. Geometry shader The idea is to extrude the vertices to their normal with a distance of the furlength. In this shader I create quads, so the maxvertexcount is set to 4. This geometry shader gets a VS_DATA in line structure, because we only need to points on the mesh surface to create a quad, where we project the fins on. I calculate the linenormal. This is the normal between the normals of two vertices. Then I calculate the quadnormal (the normal of new formed quad). This is done by the crossproduct of the linenormal and the line. 9

11 In the geometry shader I use the CreateVertex method. The CreateVertex method, creates a vertex based on the given parameters (position, normal, texcoord, layerindex) and appends this vertex to the trianglestream. It is executed 4times (once for each vertex). After this the tristream will restart so the strip is able to add new quads. Pixel shader The fin pixelshader is basic. I create a diffusecolor. Then I calculate some shadow and multiply the shadow with the diffusecolor. I have implemented diffusescaleuv this gives you the ability to tile the textures. I add furopacity this furopacity I sample from the fin opacity texture. In the end of the pixelshader I say that when the alpha value is less than 0.15f, I discard the pixel from the further process. Finally I return the diffusecolor. 10

12 Pass 3: Generate and drawing the shells In pass3, I generate and draw the shells. First I set the rasterizerstate to noneculling, we want to see both sides of the quads. Vertex shader In this vertex shader I pass the data on to the geometry shader. Geometry shader The idea is to extrude the triangles of the mesh along their normal over a certain distance. First I set the maxvertexcount to (30*3). The for loop goes over every layer and generates a new triangle for each layer. The loop inside the first for loop adds an offset to the positions of the vertices of the triangle. So the new triangle is generated above the previous triangle. When I create the vertices of the new triangle I also add gravity, force 1 and force 2 to the vertices. I have 3 sliders, with these slider I can control the strength of the forces on the hairs. You can generate every possible direction and strength of forces with these 3 sliders. 11

13 In the geometry shader I use the CreateVertex method. The CreateVertex method, creates a vertex based on the given parameters (position, normal, texcoord, layerindex) and appends this vertex to the trianglestream. Pixel shader The shell pixel shader is basic I create a diffusecolor. Then I sample the diffusecolor from the diffusetexture. I have implemented diffusescaleuv and opacityscaleuv, this gives you the ability to tile the textures. I add fur opacity, this fur opacity I sample from the shell opacity texture. I put the fur opacity in the alpha channel from the diffusecolor. In the end, I say when the alpha value is higher than 1.0f, the alpha value is always 1.0f. When the alpha value is lower than 0.2f, I discard the pixel from the further process. Finally I return the diffusecolor. 12

14 Final result Here is a shot of my fur shader. Conclusion In the end, I am happy with the result of my fur shader and my paper. I think the result looks like real fur. The shader is not high end but I think I achived a good result. Future improvements o o Make the clumping of the fur better, more changeable Implementing in the engine References info and example of rendering fur