Tutorial 3 - Lights

Tutorial 3 - Lights
This tutorial assumes you have a basic understanding of "4D Blue" functions, especially that you know how to move, adjust and rename objects. In this tutorial we will start from an existing simple scene and by using various lights and adjusting their parameters see how a very different lighting situations can be created with "4D Blue". Please be aware that lights are still being constantly updated and in the future they are likely to change and be optimized.
Step 1 - Creating or loading the simple scene.
	In this tutorial, you can either create your own simple scene or preload an existing one. If you decide to create your own scene, make sure that it has at least few objects with various materials, and a single camera. If you decide to use the existing scene please download it now Download "Tutorial 3" sample scene.
Step 2 - Light types.
	"4D Blue" right now supports six different light types. Some of them are fairly simple and very fast and some can get very complicated and expensive during rendering. In the following steps, each one of them will be explained in detail and demonstrated by an example.
Step 3 - Explaining light parameters.
	When you create a new light, the light constructor contains 4 different tabs. The first one "General" specifies the most important light parameters like the light type, color, intensity, and so on. Based on the light type some of the parameters might be enabled or disabled in all of the tabs as they are not needed or used. - "Max Range" specifies what the maximum range is at which the light should illuminate the surface. It only applies to lights that have clearly specified positions like point or spot lights. - "Enabled" controls whether the light should be used. It is often handy to quickly turn the lights off and on to see how they affect the scene rather than adjust any other parameters. - "Allow Over-Exposure" controls whether the light value can exceed 1.0 - i.e. the light can be infinity bright at near distances. Sometimes it is desirable and sometime sit is not. - "Cast Shadows" control whether the light cast shadows. - "Decay Rate" controls at what rate the light intensity fades based on the distance. - "Intensity" specifies how bright the light is. - "Fade Distance" is only used if the "Use Fade Distance Model" flag is set. It specifies at what distance the light should have the specified intensity. It is the model that POV-Ray uses.
	- "Cone Angle" specifies how wide the spotlight full attenuation area is. - "Penumbra Angle" specifies at what maximum angle the light attenuation falls to zero. - "Texture" specifies whether the light should use a texture rather than the specified color to illuminate the surfaces. - "Aspect Ratio" and "Roll" are only used if a texture and a spotlight are used at the same time. They control how projection texture should be adjusted. Sometimes the projection texture is not square and the aspect ratio needs to be adjusted, and “Roll” controls whether the texture should be rotated and by how much.
	- "Min Samples" controls what the minimum number of samples tested are for area lights. Sampling area lights is a two step process. First the minimum number of samples is tested and if all the samples are in shade or are lighted, further sampling is not needed and the point is assumed to not be in the "penumbra" range. Otherwise, the full number of samples is used to determine the light attenuation at a given point. Usually “Max Samples” should be about 4 times more than the minimum samples number. Adjust these numbers until the quality of the soft shadows satisfies your requirements. The more the samples, the better the result, but the longer it takes. - "Size" is used only for simple area lights that can be used with point or spot lights. It creates a virtual sphere of the specified size and uses points on it to evaluate the light contribution. - "Jitter Samples" controls whether the samples on the sphere should be regular or randomly picked. - "Poly Object" is used for lights that are not often well defined and need to be more constrained. It can be used with "Object Lights", "Directional Lights", and "Sky Lights". For "Object Lights", it specifies the light source object, while the other two lights serve as filter - i.e. only light rays that pass through the object will illuminate the surface. That property is very handy during Global Illumination simulations. - "Use Vertex Color" specifies whether the light color or the object vertex color should be used as a light color.
	Global Illumination parameters will be explained more in the GI Tutorial. - "Sample Rays" control the number of rays that are used to sample the environment surrounding the intersection point to evaluate the light intensity. - "Sky Up Vector" specifies the direction that the sky top is pointing. - "Sky Lighting Model" specifies which lighting model should be used. Sunny day and partly cloudy day models also need additional sun direction vectors. - "Trace Lights Rays" specifies whether the illumination should be evaluated by tracing rays through the scene. It gives the best and the most accurate result, but can be very expensive. I already have few ideas on how to speed it up in the future but for now it is slow.
Step 4 - Ambient Light
	Ambient light is used to specify the minimum amount of light that reaches every point in the scene. It is clearly only used when full GI simulation is not used and ambient light are in fact disabled when Global Illumination is enabled. Ambient intensity is only specified by the light color.
	For this test adjust the color value to about 70.
	The scene in the preview should look like the one on the left image.
	Here is the final rendering with only ambient light. No shadows are present and the scene looks plain.
Step 5 - Point Lights
	Unlike ambient lights, point lights are clearly specified in the space. For this example, move the light to (1, 3, -2). Also reduce the existing ambient light value to about 40.
	Adjust the light intensity until you are satisfied. I think a value between 3 and 6 should be a good one.
	Here is the final rendering with ambient and point light. The image clearly looks better with the objects’ shapes being well defined. The shadows also help the eyes to clearly place the objects in the space.
Step 6 - Using soft shadows with point and spot lights.
	Using the existing point light, adjust the area parameters to the ones like on the left image.
	The soft shadows will not be rendered until we also turn them on in the "Rendering Setup".
	The image looks almost like the previous one with the exception that the shadows are no longer sharp. They are in fact nicely soft.
Step 7 - Setting up Spot Lights.
	Delete the ambient light as we no longer need it. Adjust the existing point light intensity to 20 and change its type to "Spot Light". Also set its area size back to 0 again. Then adjust the light "Look At" vector.
	The "Look At" vector specifies the direction at which the light is pointing. A vector (-0.15, 0.5, 0.3) seems to be pretty good.
	Finally adjust the spotlight properties as shown on the left image.
	Spotlight allows us to nicely narrow down the area where the light has an effect. They are very practical as most real life lights are like that.
Step 8 - Using a projection texture.
	Create a new "2D Bitmap" texture and name it "Texture Bitmap". Load your favorite image map.
	Set up your newly created texture in the light constructor. You might need to select another object and then select the light again in order for the texture to be available in the combo box (an existing bug).
	Using a texture with a spotlight can produce very interesting light environment. A simpler black and white filter could also be used to produce spotlights of all possible shapes.
Step 9 - Creating a Directional Light.
	Directional lights are very useful for simulating distant lights, for example, the sun. They don't have a specified point in space, but they have a direction. Enter (-0.5, -0.5, -0.6) for the "Look At" vector for the light.
	Switch to "Directional Light". Notice that you can no longer specify decay rate as the light intensity doesn’t change. Adjust the intensity to 1.0
	Directional Light gives very straight shadows and no decay in the light intensity.
Step 10 - Creating an Object Light.
	Object Lights use an existing object in the scene as a light source. This way you can have lights of all kinds of shapes and orientations. Start with creating a polygonal plane object. Use the dimensions from the left image.
	Adjust the new object positions to (0.0, 5.0, -1.0). To make the preview look as close as possible to the final rendered image adjust the light position to the center of the object also at (0.0, 5.0, -1.0). The quick D3D preview can’t handle such complex light type so it is still using the light position even that it will not be used during the final render.
	The view from the top should look like the one on the left image.
	Set the light type to "Object Light". Select the newly created object in the "Poly Object" combo box. You might need to reselect the light (again a small bug). You will need to adjust the "Min Samples" and "Max Samples" to achieve a satisfying quality. Usually the larger the object, the more samples are need. Our object is fairly large, and I would start with 16 and 64 for min and max numbers.
	Adjust the intensity again to 20.0
	The rendered image produced good soft shadows, but they are bit noisy. That could be reduced using more samples at a cost of longer rendering times. As you notice, the specular highlights are not very accurate as our light is no longer a sphere like light. The problem is that specular highlight is a fairly artificial thing to begin with.
	By changing the shaders and assigning an ambient material to the light object, we can achieve more realistic specular highlights. But that would be beyond the scope of this tutorial.
Step 11 - Sky Lights
	Sky Lights work by sampling a hemisphere above the surface point and evaluating the light contribution from all directions on that hemisphere. There are many models used to evaluate the value of each of the sample points on the hemisphere. Some of these methods simulate real sun light intensity distribution, and they need a direction vector to the sun. Always place sky light at the origin. Then adjust the "Look At" Point to point in the direction of the sun.
	Experiment with different sky light types and see how they work. For some you might need to adjust the intensity of the light until you achieve a desired effect.
	A "Cloudy Day" Sky light.
	A "Clear Sky" Sky light.
Step 12 - Using HDR Textures with Sky Lights.
	For this step you will need a HDR light probe. They are fairly difficult to create, but fortunately a few very good probes can be found on Paul Debevec web site: Light Probes. Install them into the HDR directory. Once that is completed, create new HDR texture and name it "Texture HDR". Load your favorite light probe. In my case, I'm using "The Grace Cathedral".
	When you load a HDR image, you can adjust the exposure ratio which specifies how bright the image is and their gamma correction. For light probes, it is also often helpful to reduce their resolution to minimize the noise in the final rendered images. Set the new texture in the "Texture" Combo box in the "Extra" tab of the light constructor.
	Here is the final rendered image. It is a bit noisy, because we only used 64 samples. Overall, the color looks like an average of all the colors present in the HDR image, but that is what we expected.
Step 13 - Using HDR Texture on a Sky Sphere.
	In this step, we are going to create a sphere that will serve us as a sky sphere. Create new polygonal sphere and adjust its constructor as shown on the left. Rename the new object as "Sky Sphere".
	In the "Nodes Toolbar", select the new object and in the context menu select "Properties...". Then turn off the cast shadows flag. We clearly don't want the sky sphere to cast any shadows.
	We need to create a new material for our sky sphere. In the material editor, create new material and rename it to "Material Sky". The material we need should not depend on the lights at all in the scene, so we are going to use "SurfaceGI AmbientTexture" material. Setup the material shader as shown on the left image.
	Select the "Sky Sphere" object and in the "Surfaces Toolbar", select all surfaces and flip their normals. The sphere is after all outside and we are looking at it from its inside.
	In the light constructor, set the "Sky Light Model" to uniform. Also enable "Trace Lights Rays" which will force the renderer to shoot rays through the scene and recursively trace them. This way, the caustics will be evaluated as well. The rendering now can really take a while.
	The final image should be like the one on the left. The Sky sphere is clearly visible in reflections, and the fact that we enabled "Trace Light Rays" gives us a nice realistic caustics on the floor, produced by the lights passing through the glass sphere.

Tutorial 3 - Lights

Step 1 - Creating or loading the simple scene.

Step 2 - Light types.

"4D Blue" right now supports six different light types. Some of them are fairly simple and very fast and some can get very complicated and expensive during rendering. In the following steps, each one of them will be explained in detail and demonstrated by an example.

Step 3 - Explaining light parameters.

- "Max Range" specifies what the maximum range is at which the light should illuminate the surface. It only applies to lights that have clearly specified positions like point or spot lights.

- "Enabled" controls whether the light should be used. It is often handy to quickly turn the lights off and on to see how they affect the scene rather than adjust any other parameters.

- "Allow Over-Exposure" controls whether the light value can exceed 1.0 - i.e. the light can be infinity bright at near distances. Sometimes it is desirable and sometime sit is not.

- "Cast Shadows" control whether the light cast shadows.

- "Decay Rate" controls at what rate the light intensity fades based on the distance.

- "Intensity" specifies how bright the light is.

- "Fade Distance" is only used if the "Use Fade Distance Model" flag is set. It specifies at what distance the light should have the specified intensity. It is the model that POV-Ray uses.

- "Cone Angle" specifies how wide the spotlight full attenuation area is.

- "Penumbra Angle" specifies at what maximum angle the light attenuation falls to zero.

- "Texture" specifies whether the light should use a texture rather than the specified color to illuminate the surfaces.

- "Size" is used only for simple area lights that can be used with point or spot lights. It creates a virtual sphere of the specified size and uses points on it to evaluate the light contribution.

- "Jitter Samples" controls whether the samples on the sphere should be regular or randomly picked.

- "Use Vertex Color" specifies whether the light color or the object vertex color should be used as a light color.

Global Illumination parameters will be explained more in the GI Tutorial.

- "Sample Rays" control the number of rays that are used to sample the environment surrounding the intersection point to evaluate the light intensity.

- "Sky Up Vector" specifies the direction that the sky top is pointing.

- "Sky Lighting Model" specifies which lighting model should be used. Sunny day and partly cloudy day models also need additional sun direction vectors.

- "Trace Lights Rays" specifies whether the illumination should be evaluated by tracing rays through the scene. It gives the best and the most accurate result, but can be very expensive. I already have few ideas on how to speed it up in the future but for now it is slow.

Step 4 - Ambient Light

Ambient light is used to specify the minimum amount of light that reaches every point in the scene. It is clearly only used when full GI simulation is not used and ambient light are in fact disabled when Global Illumination is enabled. Ambient intensity is only specified by the light color.

For this test adjust the color value to about 70.

The scene in the preview should look like the one on the left image.

Here is the final rendering with only ambient light. No shadows are present and the scene looks plain.

Step 5 - Point Lights

Unlike ambient lights, point lights are clearly specified in the space. For this example, move the light to (1, 3, -2). Also reduce the existing ambient light value to about 40.

Adjust the light intensity until you are satisfied. I think a value between 3 and 6 should be a good one.

Here is the final rendering with ambient and point light. The image clearly looks better with the objects’ shapes being well defined. The shadows also help the eyes to clearly place the objects in the space.

Step 6 - Using soft shadows with point and spot lights.

Using the existing point light, adjust the area parameters to the ones like on the left image.

The soft shadows will not be rendered until we also turn them on in the "Rendering Setup".

The image looks almost like the previous one with the exception that the shadows are no longer sharp. They are in fact nicely soft.

Step 7 - Setting up Spot Lights.

Delete the ambient light as we no longer need it. Adjust the existing point light intensity to 20 and change its type to "Spot Light". Also set its area size back to 0 again. Then adjust the light "Look At" vector.

The "Look At" vector specifies the direction at which the light is pointing. A vector (-0.15, 0.5, 0.3) seems to be pretty good.

Finally adjust the spotlight properties as shown on the left image.

Spotlight allows us to nicely narrow down the area where the light has an effect. They are very practical as most real life lights are like that.

Step 8 - Using a projection texture.

Create a new "2D Bitmap" texture and name it "Texture Bitmap". Load your favorite image map.

Set up your newly created texture in the light constructor. You might need to select another object and then select the light again in order for the texture to be available in the combo box (an existing bug).

Using a texture with a spotlight can produce very interesting light environment. A simpler black and white filter could also be used to produce spotlights of all possible shapes.

Step 9 - Creating a Directional Light.

Directional lights are very useful for simulating distant lights, for example, the sun. They don't have a specified point in space, but they have a direction. Enter (-0.5, -0.5, -0.6) for the "Look At" vector for the light.

Switch to "Directional Light". Notice that you can no longer specify decay rate as the light intensity doesn’t change. Adjust the intensity to 1.0

Directional Light gives very straight shadows and no decay in the light intensity.

Step 10 - Creating an Object Light.

Object Lights use an existing object in the scene as a light source. This way you can have lights of all kinds of shapes and orientations. Start with creating a polygonal plane object. Use the dimensions from the left image.

The view from the top should look like the one on the left image.

Adjust the intensity again to 20.0

By changing the shaders and assigning an ambient material to the light object, we can achieve more realistic specular highlights. But that would be beyond the scope of this tutorial.

Step 11 - Sky Lights

Experiment with different sky light types and see how they work. For some you might need to adjust the intensity of the light until you achieve a desired effect.

A "Cloudy Day" Sky light.

A "Clear Sky" Sky light.

Step 12 - Using HDR Textures with Sky Lights.

Here is the final rendered image. It is a bit noisy, because we only used 64 samples. Overall, the color looks like an average of all the colors present in the HDR image, but that is what we expected.

Step 13 - Using HDR Texture on a Sky Sphere.

In this step, we are going to create a sphere that will serve us as a sky sphere. Create new polygonal sphere and adjust its constructor as shown on the left. Rename the new object as "Sky Sphere".

In the "Nodes Toolbar", select the new object and in the context menu select "Properties...". Then turn off the cast shadows flag. We clearly don't want the sky sphere to cast any shadows.

Select the "Sky Sphere" object and in the "Surfaces Toolbar", select all surfaces and flip their normals. The sphere is after all outside and we are looking at it from its inside.

In the light constructor, set the "Sky Light Model" to uniform. Also enable "Trace Lights Rays" which will force the renderer to shoot rays through the scene and recursively trace them. This way, the caustics will be evaluated as well. The rendering now can really take a while.

The final image should be like the one on the left. The Sky sphere is clearly visible in reflections, and the fact that we enabled "Trace Light Rays" gives us a nice realistic caustics on the floor, produced by the lights passing through the glass sphere.