openframeworks 使用glslsandbox里面的shader

</pre>glslsandbox里面有很多很炫酷的shader，把它用在程序中有一个很简单的方法。<p></p><p>利用openframeworks的addon：ofxGLSLSandbox。</p><p>glsl官网：http://glslsandbox.com/。</p><p>插件地址：http://www.ofxaddons.com/。</p><p>首先把glslsandbox网站上你喜欢的效果的代码复制到shader文件中：</p><p><pre name="code" class="cpp">#ifdef GL_ES
precision mediump float;
#endif

//Mode7 test

uniform float time;
uniform vec2 mouse;
uniform vec2 resolution;
void main( void ) {

vec2 position = ( gl_FragCoord.xy / resolution.xy );
//x' = (a*x-x0)+(b*y-y0)+x0
//y' = (c*x-x0)+(d*y-y0)+y0
vec2 origin = vec2(0.5,0);
vec2 delta = position - origin;
vec4 transMat = vec4(4.0,0.0,0.0,1.0);

vec2 transform = vec2(
transMat.x * delta.x + transMat.y * delta.y + origin.x,
transMat.z * delta.x + transMat.w * delta.y + origin.y);
vec2 persp = vec2(
(0.5-transform.x)/(1.0-transform.y),
1.0/(1.0-transform.y));
mat2 rot = mat2(
cos(time),-sin(time),
sin(time),cos(time)
);
vec2 post = persp * rot; //+ vec2(sin(time),time*2.0) +

if(position.y < persp.y)
gl_FragColor = vec4(vec3(sin(post.x * 15.0),sin(post.y * 15.0),0.0),1.0);
else
gl_FragColor = vec4(0.7,0.7,1.0,1.0);
}

在openframeworks的项目中：

一：初始化glslsandbox

width = _width;
height = _height;
fbo.allocate(width, height);

shader画在fbo里面，先定义fbo的大小。

二：载入shader：

shader.load(shaderfile);
string command = "open ../../../data/" + shaderfile;
system(command.c_str());

三：把为shader里面的变量复制并绘制：

float resolution[] = {width, height};
float mousePoint[] = {mouse.x, mouse.y};
float time = ofGetElapsedTimef();

fbo.begin();
shader.begin();
shader.setUniform1f("time", time);
shader.setUniform2fv("resolution", resolution);
shader.setUniform2fv("mouse", mousePoint);
ofRect(0, 0, ofGetWidth(), ofGetHeight());
shader.end();
fbo.end();

fbo.draw(0, ofGetHeight(), ofGetWidth(), -ofGetHeight());

我们可以通过控制shader的参数来改变shader的效果，openframeworks中update（）优化了参数的运算，所以最好是在update（）中去改变传值，draw（）方法优化绘制，然后在draw中去绘制shader。

by：zxy