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CIS565: Project 6: Deferred Shader

Fall 2013

INTRODUCTION:

In this project, the basics of deferred shading are implemented. GLSL and OpenGL code is written to perform various tasks in a deferred lighting pipeline such as creating and writing to a G-Buffer.

The following have been implemented:

  • Bloom
  • An additional G buffer slot and some effect showing it off To create this effect, a new G-Buffer object called Bloom was added, similar to how other g-buffer objects were added ,the same procedure was followed. A bloom texture was added and it stored 0 or 1 based on the material value. And then a gaussian filter was created which took the average of the neighbouring 5*5 pixels and averaged the value according to gaussian distribution. A new fragmnet shader called bloom.frag was created and all the bloom fragment operations were written inside it.
  • Point light sources To create point lights a number of point light locations were created and the draw light function was called. Inside point.frag a condition was provided to take the point light strength and that there was linear fall-off in the intensity of light emitted by the point light.

The following extra features have been implemented:

  • "Toon" Shading (with basic silhouetting) Toon shading with basic silhoutting was implemented inside post.frag as a post process effect. In order to get the toon colors, the input colors were clamped to a certain range and hence resulted in tool like effect. In order to get the silhouetting to work , each pixel was taken and the neighbouring 3*3 pixels were considered to find the x-gradient and y-gradient , using which the slope of the edge was calculated. A particular threshold was choosen and if less than the threshold, the pixel was colored black ,else it was given the toon color.

  • "Mosaic" Shading In order to Implement mosaic shading , each pixel was considered and the goal was to assign the same color to the next 1010 pixels, even though each fragment was getting its own color, it had replace that color with the first color of the 1010 kernel. To do this each texture co-ordinate was considered and multiplied with screen width and height. then this value was divided by 10 and the floor was taken. The floored value was again divided by screen width and height and multiplied again by 10, so effectively all the co-ordinated of the texture were floored to a certain value to put the same color to other pixels.

  • "Fish eye effect" To create the fish eye effect, the texture co-ordinates were taken and it was projected on to a hemisphere and then the field of view was considered to provide the distortion factor ,which inturn is used to calculate the new texture co-ordinates to be used for that particular pixel .The following link was followed to implement the fish eye effect , http://gamedev.stackexchange.com/questions/27728/how-to-implement-fisheye-effect-with-a-glsl-fragment-shader

  • Emboss effect Not working in the current scene, but the code is written for the Emboss effect. Emboss is a popular effect in video editing and it compares the color of the neighbouring pixel and difference in coor is added with a grey scale value which inturn provides a depth like feature. In order for this effect to work we need many colors like in a photograph, but since the diffuse colors remain very close to each other , the subtraction between neighbouring pixels makes the image completely gray due to lack of variations in pixels.

VIDEO

Deferred Shading Video

RENDERS

With diffuse lighting alt tag

With Bloom effect applied alt tag

With toon shading applied alt tag

With toon shading applied on Sponza scene alt tag

With mozaic shading applied alt tag

With fish eye effect applied alt tag

With fish eye effect applied on Sponza scene alt tag

PERFORMANCE EVALUATION

For performance evaluation of deferred shading, the frame rates for different effects were noted and compared. As the computations in the shaders for the effects became complex, the frames rates dropped.

Here are the frame rate comparisons for different effects:

	Effect		       Frame rate
    Basic Diffuse 	         37.22
     With Bloom               2.69     
    Toon Shading             36.45
   Mosaic Shading            37.11
   Fish eye effect           37.29

In Bloom shading the as the kernel size for averaging incresed the frame rate decresed drastically because of more computations and for toon shading , since in toon shading many comparisons in colors was involved the frame decreased a bit.