Implementing per-fragment spot light
by William C. Y. Lo, Raymond C. H. Lo, David Wolff, Muhammad Mobeen Movania
OpenGL – Build high performance graphics
- OpenGL – Build high performance graphics
- Table of Contents
- OpenGL – Build high performance graphics
- OpenGL – Build high performance graphics
- Credits
- Preface
- 1. Module 1
- 1. Introduction to Modern OpenGL
- Introduction
- Setting up the OpenGL v3.3 core profile on Visual Studio 2010 using the GLEW and freeglut libraries
- Designing a GLSL shader class
- Rendering a simple colored triangle using shaders
- Doing a ripple mesh deformer using the vertex shader
- Dynamically subdividing a plane using the geometry shader
- Dynamically subdividing a plane using the geometry shader with instanced rendering
- Drawing a 2D image in a window using the fragment shader and the SOIL image loading library
- 2. 3D Viewing and Object Picking
- Introduction
- Implementing a vector-based camera with FPS style input support
- Implementing the free camera
- Implementing the target camera
- Implementing view frustum culling
- Implementing object picking using the depth buffer
- Implementing object picking using color
- Implementing object picking using scene intersection queries
- 3. Offscreen Rendering and Environment Mapping
- Introduction
- Implementing the twirl filter using the fragment shader
- Rendering a skybox using static cube mapping
- Implementing a mirror with render-to-texture using FBO
- Rendering a reflective object using dynamic cube mapping
- Implementing area filtering (sharpening/blurring/embossing) on an image using convolution
- Implementing the glow effect
- 4. Lights and Shadows
- Introduction
- Implementing per-vertex and per-fragment point lighting
- Implementing per-fragment directional light
- Implementing per-fragment point light with attenuation
- Implementing per-fragment spot light
- Implementing shadow mapping with FBO
- Implemeting shadow mapping with percentage closer filtering (PCF)
- Implementing variance shadow mapping
- 5. Mesh Model Formats and Particle Systems
- 6. GPU-based Alpha Blending and Global Illumination
- Introduction
- Implementing order-independent transparency using front-to-back peeling
- Implementing order-independent transparency using dual depth peeling
- Implementing screen space ambient occlusion (SSAO)
- Implementing global illumination using spherical harmonics lighting
- Implementing GPU-based ray tracing
- Implementing GPU-based path tracing
- 7. GPU-based Volume Rendering Techniques
- Introduction
- Implementing volume rendering using 3D texture slicing
- Implementing volume rendering using single-pass GPU ray casting
- Implementing pseudo-isosurface rendering in single-pass GPU ray casting
- Implementing volume rendering using splatting
- Implementing transfer function for volume classification
- Implementing polygonal isosurface extraction using the Marching Tetrahedra algorithm
- Implementing volumetric lighting using the half-angle slicing
- 8. Skeletal and Physically-based Simulation on the GPU
- Introduction
- Implementing skeletal animation using matrix palette skinning
- Implementing skeletal animation using dual quaternion skinning
- Modeling cloth using transform feedback
- Implementing collision detection and response on a transform feedback-based cloth model
- Implementing a particle system using transform feedback
- 1. Introduction to Modern OpenGL
- 2. Module 2
- 1. Getting Started with GLSL
- Introduction
- Using a function loader to access the latest OpenGL functionality
- Using GLM for mathematics
- Determining the GLSL and OpenGL version
- Compiling a shader
- Linking a shader program
- Sending data to a shader using vertex attributes and vertex buffer objects
- Getting a list of active vertex input attributes and locations
- Sending data to a shader using uniform variables
- Getting a list of active uniform variables
- Using uniform blocks and uniform buffer objects
- Getting debug messages
- Building a C++ shader program class
- 2. The Basics of GLSL Shaders
- Introduction
- Implementing diffuse, per-vertex shading with a single point light source
- Implementing per-vertex ambient, diffuse, and specular (ADS) shading
- Using functions in shaders
- Implementing two-sided shading
- Implementing flat shading
- Using subroutines to select shader functionality
- Discarding fragments to create a perforated look
- 3. Lighting, Shading, and Optimization
- 4. Using Textures
- 5. Image Processing and Screen Space Techniques
- 6. Using Geometry and Tessellation Shaders
- 7. Shadows
- 8. Using Noise in Shaders
- 9. Particle Systems and Animation
- 10. Using Compute Shaders
- 1. Getting Started with GLSL
- 3. Module 3
- 1. Getting Started with OpenGL
- Introduction
- Setting up a Windows-based development platform
- Setting up a Mac-based development platform
- Setting up a Linux-based development platform
- Installing the GLFW library in Windows
- Installing the GLFW library in Mac OS X and Linux
- Creating your first OpenGL application with GLFW
- Compiling and running your first OpenGL application in Windows
- Compiling and running your first OpenGL application in Mac OS X or Linux
- 2. OpenGL Primitives and 2D Data Visualization
- 3. Interactive 3D Data Visualization
- 4. Rendering 2D Images and Videos with Texture Mapping
- Introduction
- Getting started with modern OpenGL (3.2 or higher)
- Setting up the GLEW, GLM, SOIL, and OpenCV libraries in Windows
- Setting up the GLEW, GLM, SOIL, and OpenCV libraries in Mac OS X/Linux
- Creating your first vertex and fragment shader using GLSL
- Rendering 2D images with texture mapping
- Real-time video rendering with filters
- 5. Rendering of Point Cloud Data for 3D Range-sensing Cameras
- 6. Rendering Stereoscopic 3D Models using OpenGL
- 7. An Introduction to Real-time Graphics Rendering on a Mobile Platform using OpenGL ES 3.0
- 8. Interactive Real-time Data Visualization on Mobile Devices
- 9. Augmented Reality-based Visualization on Mobile or Wearable Platforms
- A. Bibliography
- 1. Getting Started with OpenGL
- Index
We will now implement per-fragment spot light. Spot light is a special point light that emits light in a directional cone. The size of this cone is determined by the spot cutoff amount, which is given in angles, as shown in the following figure. In addition, the sharpness of the spot is controlled by the parameter spot exponent. A higher value of the exponent gives a sharper falloff and vice versa.
The code for this recipe is contained in the Chapter4/SpotLight directory. The vertex shader is the same as in the point light recipe. The fragment shader calculates the diffuse component, as in the Implementing per-vertex and per-fragment point lighting recipe.
Let us start this recipe by following these simple steps:
- From the light's object space position and spot light target's position, calculate the spot light direction vector in eye space.
spotDirectionES = glm::normalize(glm::vec3(MV*glm::vec4(spotPositionOS-lightPosOS,0)))
- In the fragment shader, calculate the diffuse component as in point light. In addition, calculate the spot effect by finding the angle between the light direction and the spot direction vector.
vec3 L = (light_position.xyz-vEyeSpacePosition); float d = length(L); L = normalize(L); vec3 D = normalize(spot_direction); vec3 V = -L; float diffuse = 1; float spotEffect = dot(V,D);
- If the angle is greater than the spot cutoff, apply the spot exponent and then use the diffuse shader on the fragment.
if(spotEffect > spot_cutoff) { spotEffect = pow(spotEffect, spot_exponent); diffuse = max(0, dot(vEyeSpaceNormal, L)); float attenuationAmount = spotEffect/(k0 + (k1*d) + (k2*d*d)); diffuse *= attenuationAmount; vFragColor = diffuse*vec4(diffuse_color,1); }
The spot light is a special point light source that illuminates in a certain cone of direction. The amount of cone and the sharpness is controlled using the spot cutoff and spot exponent parameters respectively. Similar to the point light source, we first calculate the diffuse component. Instead of using the vector to light source (L) we use the opposite vector, which points in the direction of light (V=-L). Then we find out if the angle between the spot direction and the light direction vector is within the cutoff angle range. If it is, we apply the diffuse shading calculation. In addition, the sharpness of the spot light is controlled using the spot exponent parameter. This reduces the light in a falloff, giving a more pleasing spot light effect.
The demo application implementing this recipe renders the same scene as in the point light demo. We can change the spot light direction using the right mouse button. The output result is shown in the following figure:
- Real-time Rendering, Third Edition, Tomas Akenine-Moller, Eric Haines, Naty Hoffman, A K Peters/CRC Press
- Spot Light in GLSL tutorial at Ozone3D: http://www.ozone3d.net/tutorials/glsl_lighting_phong_p3.php
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