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| public:t-vien-08-1:lab_7_materials [2008/02/21 06:34] – hannes | public:t-vien-08-1:lab_7_materials [2024/04/29 13:33] (current) – external edit 127.0.0.1 |
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| ==== Writing a Shader ==== | ==== Writing a Shader ==== |
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| - **The simplest shader:**\\ Make sure you can run **testshader.py** and that you can see a white teapot on the screen. The color blue is being passed into the shader through the **tint** constant. Try different color values for this constant. Then open up **myshader.sha** and notice how the value is used in the vertex shader to assign a color to a vertex. Play with the color values inside the vertex shader and see how it affects the final render. | - **The Simplest Shader:**\\ Make sure you can run **testshader.py** and that you can see a white teapot on the screen. The color blue is being passed into the shader through the **tint** constant. Try different color values for this constant. Then open up **myshader.sha** and notice how the value is used in the vertex shader to assign a color to a vertex. Play with the color values inside the vertex shader and see how it affects the final render. |
| - **Diffuse Vertex Shading:**\\ Instead of sending a preset color value to all of the vertices inside the vertex shader, let the vertex shader calculate the color in each vertex based on a lighting model. Use the following lighting model to do this calculation: **color = 0.2*ambientcolor + diffuse_attenuation*diffusecolor + specular_attenuation*specularcolor**. Instead of *tint* you now have to send **ambientcolor**, **diffusecolor** and **specularcolor** into the shader. Inside the vertex shader, you then have to calculate the **diffuse_attenuation** and **specular_attenuation** which are values between 0 and 1 that indicate how much of that color will be seen in that vertex.\\ | - **Diffuse Vertex Shading:**\\ Instead of sending a preset color value to all of the vertices inside the vertex shader, let the vertex shader calculate the color in each vertex based on a lighting model. Use the following lighting model to do this calculation: **color = 0.2*ambientcolor + diffuse_attenuation*diffusecolor + specular_attenuation*specularcolor**. Instead of *tint* you now have to send **ambientcolor**, **diffusecolor** and **specularcolor** into the shader. Inside the vertex shader, you then have to calculate the **diffuse_attenuation** and **specular_attenuation** which are values between 0 and 1 that indicate how much of that color will be seen in that vertex.\\ |
| - The **diffuse_attenuation** essentially represents how well the vertex is lit, which relates to the angle between the vertex normal and the direction to the light source. This is the formula (using Cg functions): **diffuse_attenuation = saturate(dot(LightVector, NormalVector))**.\\ | - The **diffuse_attenuation** essentially represents how well the vertex is lit, which relates to the angle between the vertex normal and the direction to the light source. This is the formula (using Cg functions): **diffuse_attenuation = saturate(dot(LightVector, NormalVector))**.\\ |
| - Now you should be able to calculate the **diffuse_attenuation**. Set the **specular_attenuation** to 0 for now and test your lighting model so far.\\ | - Now you should be able to calculate the **diffuse_attenuation**. Set the **specular_attenuation** to 0 for now and test your lighting model so far.\\ |
| - **Specular Vertex Shading:**\\ Now calculate the **specular_attenuation** value in the lighting model. The formula for this is: **specular_attn = pow(saturate(dot(ReflectionVector,ViewVector)),6.0)**. This essentially says that this component will get a sharp increase (by raising the results to the power of 6) when the reflection of the light lines up with the direction towards our eyes. Just like you needed the light position passed in to calculate the LightVector, you'll need to pass in the camera position to calculate the ViewVector. Once you've gotten the ViewVector, you need to calculate the light ReflectionVector with this formula: R=normalize(2*N*dot(N,L)-L). Try to make this specular lighting work in your shader. | - **Specular Vertex Shading:**\\ Now calculate the **specular_attenuation** value in the lighting model. The formula for this is: **specular_attn = pow(saturate(dot(ReflectionVector,ViewVector)),6.0)**. This essentially says that this component will get a sharp increase (by raising the results to the power of 6) when the reflection of the light lines up with the direction towards our eyes. Just like you needed the light position passed in to calculate the LightVector, you'll need to pass in the camera position to calculate the ViewVector. Once you've gotten the ViewVector, you need to calculate the light ReflectionVector with this formula: R=normalize(2*N*dot(N,L)-L). Try to make this specular lighting work in your shader. |
| - **Diffuse and Specular Pixel Lighting :**\\ So far you have only been calculating the color values for each of the vertices in a model, which can result in rough lighting artifacts (occurs when simple interpolation of vertex colors is not enough). To prevent these artifacts, you can move the lighting calculation inside the pixel/fragment shader and perform them for each pixel. You do not have to calculate the Vectors inside the pixel shader; if you pass these vectors into the pixel shader from the vertex shader using the TEXCOORD semantics (registers), they will be correctly interpolated. Dot products don't interpolate, so that's why the final calculations have to take place inside the pixel shader. See if you can now create per-pixel diffuse and specular lighting. Notice how much better looking it is than the per-vertex lighting (but also realize that this is more GPU intensive). | - **Diffuse and Specular Pixel Shading:**\\ So far you have only been calculating the color values for each of the vertices in a model, which can result in rough lighting artifacts (occurs when simple interpolation of vertex colors is not enough). To prevent these artifacts, you can move the lighting calculation inside the pixel/fragment shader and perform them for each pixel. You do not have to calculate the Vectors inside the pixel shader; if you pass these vectors into the pixel shader from the vertex shader using the TEXCOORD semantics (registers), they will be correctly interpolated. Dot products don't interpolate, so that's why the final calculations have to take place inside the pixel shader. See if you can now create per-pixel diffuse and specular lighting. Notice how much better looking it is than the per-vertex lighting (but also realize that this is more GPU intensive). |
| - **Texture:**\\ The **teapot** model doesn't have any texture coordinates, so for this step you'll need to switch to a different model (a sphere and a car are provided). First make sure that your current shader works with your new model. The next step is to replace the **diffusecolor** in your lighting model with the color sampled from a texture. First, load the texture you want into Panda and assign it to the model PathNode (The textures are in Models/Textures). It's a good idea to explicitly create a texture stage (a texture channel) for the texture, although this is not needed if you only want to use a single texture. Example: <code python> | - **Texture:**\\ The **teapot** model doesn't have any texture coordinates, so for this step you'll need to switch to a different model (a sphere and a car are provided). First make sure that your current shader works with your new model. The next step is to replace the **diffusecolor** in your lighting model with the color sampled from a texture. First, load the texture you want into Panda and assign it to the model PathNode (The textures are in Models/Textures). It's a good idea to explicitly create a texture stage (a texture channel) for the texture, although this is not needed if you only want to use a single texture. Example: <code python> |
| diffusecolormap = loader.loadTexture("./Models/Textures/bricks.png") | diffusecolormap = loader.loadTexture("./Models/Textures/bricks.png") |
