International Graphics Workshop 2014 at Trident College of Information Technology from July 1st to July 29th in 2014.

1. International 5-days Graphics
Programming Workshop
using Cocos-2d-x
DAY 5
Trident College of Information Technology
Takao WADA

2. 1. Review
2. Toon Shading
3. Alpha blending
4. Play with shader program
5. Final work
6. Presentation
Agenda

3. Review
Normal
Tangent
Bi-normal
 Normal mapping
 Tangent space
 TBN matrix
 Parametric surface
 Plane
 Sphere
 Klein bottle
 Torus

4.  Like a cartoon, cell shading
Toon shading

5.  Final color is changed into the intensity.
Toon shading (cont’d)
varying float v_intensity;
void main()
{
vec4 color;
if (v_intensity > 0.95)
color = vec4(1.0,0.5,0.5,1.0);
else if (v_intensity > 0.5)
color = vec4(0.6,0.3,0.3,1.0);
else if (v_intensity > 0.25)
color = vec4(0.4,0.2,0.2,1.0);
else
color = vec4(0.2,0.1,0.1,1.0);
gl_FragColor = color;
}
Snip…
varying float v_intensity;
void main()
{
// Set the transformed position
gl_Position = u_projectionMatrix * u_viewMatrix
* u_worldMatrix * a_position;
// Normal vector in view space
vec3 N = normalize((u_normalMatrix *
vec4(a_normal, 1)).xyz);
v_intensity = max(0.0, dot(N, vec3(0, 0, 1)));
}
Vertex shader Fragment shader

6.  Normal mapping and parametric surfaces
 Draw a Klein bottle (revised)
 Draw a torus
 Toon shading
 Draw a torus
 Change the color or the rage
Work 5-1

7. Test in the rendering pipeline
Scissor
Test
Alpha
Test
Stencil
Test
Depth
Test
Alpha
Blending
Fragment
Frame
Buffer
Dithering Logicop

8.  Scissor test
 Within the scissor rectangle defined by 4 values.
 Alpha test
 Comparison between the incoming fragment’s alpha value and a constant
value
 Stencil test
 Comparison between the value in the stencil buffer and a reference value.
 Depth test
 Depth comparison
 Alpha blending
 Blend combines the incoming source fragment with the destination fragment.
 Dithering
 Selects between two color values.
 Logical operation
 applied between the incoming fragment’s color values and the color values
stored at the corresponding location in the framebuffer.
Test in the rendering pipeline
(cont’d)

9.  Alpha blending
 Combine images or colors (Opaque -> Transparent)
 glEnable(GL_BLEND);
 glBlendFunc(src, dst);
 CB = src * Cs + dst * Cd
 Multiplicative blending (Standard)
 (alpha * src) + (1 – alpha) * dst
 src: GL_SRC_ALPHA
 dst: GL_ONE_MINUS_SRC_ALPHA
 Additive blending
 src + dst
 src: GL_ONE
 dst: GL_ONE
Add transparency using alpha
blending

10.  Main functions
Blending function
Function RGB Blend Factor Alpha blend factor
ZERO (0, 0, 0) 0
ONE (1, 1, 1) 1
SRC_COLOR (Rs, Gs, Bs) As
ONE_MINUS_SRC _COLOR (1 - Rs, 1 - Gs, 1 - Bs) 1 − As
SRC_ALPHA (As, As, As) As
ONE_MINUS_SRC_ALPHA (1 - As, 1 - As, 1 - As) 1 − As

11.  Pass the time parameter to the shader
 Pass a float value as an uniform variable
 getGLProgramState()->setUniformFloat("u_time", _time);
 Vertex shader
 uniform float u_time;
 Dynamic controls
 Change the color in a shader
 Change the form by transforming vertices
 Change the texture coordinates
Dynamic controls in shaders

12.  Add transparency
 NewParametricShaderNode class
 update function
 getGLProgramState()->setUniformFloat("u_time", _time);
 onDraw function (Override ParametericSurface’s)
 glEnable(GL_BLEND);
 glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
 alpha.vsh (Copy from lambert.vsh)
 v_diffuseColor = vec4(color, 0.5);
 Fade in / fade out
 For objects (alpha.vsh)
 uniform float u_time;
 float alpha = clamp(sin(u_time), 0.0, 1.0) ;
 For background (simple.vsh)
Work 5-2

13.  Modify the form of a shape
 vertexsin.vsh (Copy from lambert.vsh)
 float z = sin(u_time + a_position.y);
 vec4 pos = a_position + vec4(0, 0, z, 1);
 gl_Position = u_projectionMatrix * u_viewMatrix * u_worldMatrix
* pos;
 Create another formation
Work 5-3

14.  Texture parameter
 glTexParameteri(GL_TEXTURE_2D,
GL_TEXTURE_WRAP_S, GL_REPEAT);
 GL_REPEAT – Use fractional value, then repeat pattern
 GL_CLAMP – Limit the range from 0 to 1
 Scrolling
 Horizontal
 v_texCoord = a_texCoord;
 v_texCoord.x += fract(u_time);
Scroll the background

15.  Scroll background
 ShaderTextureNode.cpp
 update function
 getGLProgramState()->setUniformFloat("u_time", _time);
 onDraw function
 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
 simple.vsh
 Uniform float u_time;
 v_texCoord = a_texCoord;
 v_texCoord.x += u_time;
Work 5-4

16.  Mosaic
 Modify texture coordinate in the fragment shader
 float grids = 2.0;
 vec2 uv = floor(v_texCoord * grids + 0.5) / grids;
Play with 2-D shading

17.  Mosaic
 mosaic.fsh (Copy from simple.fsh)
 Noise
 noisy.fsh
 Gray scale
 greyscale.fsh
Work 5-5

18.  Create a graphics demo using some shapes and
shaders.
 Add some objects in the scene
 Move, rotate, scale shapes
 Dynamically, change the scene
 Present each other
Final work

19.  OpenGL ES Shader program requires a precision
qualifier
 lowp vec4 v_color; // for colors
 mediump vec2 v_texCoords; // for positions and texture
coordinates
 highp vec4 pos; // for some positions and
time
 Reference page
 http://www.khronos.org/opengles/2_X/
For OpenGL ES

20.  Sample source code
 https://github.com/drjiro/WSSample
Resources