Graphics Reference
In-Depth Information
In addition, each explosion has several global settings that are passed in as
uniforms:
•
Center position
—The center of the explosion (the per-vertex
positions are offset from this center).
•
Color
—An overall color for the explosion.
•
Time
—The current time in seconds.
With this information, the vertex and fragment shaders are completely
responsible for the motion, fading, and rendering of the particles. Let's
begin by looking at the vertex shader code for the sample in Example 14-5.
Example 14-5
Particle System Vertex Shader
#version 300 es
uniform float u_time;
uniform vec3 u_centerPosition;
layout(location = 0) in float a_lifetime;
layout(location = 1) in vec3 a_startPosition;
layout(location = 2) in vec3 a_endPosition;
out float v_lifetime;
void main()
{
if ( u_time <= a_lifetime )
{
gl_Position.xyz = a_startPosition +
(u_time * a_endPosition);
gl_Position.xyz += u_centerPosition;
gl_Position.w = 1.0;
}
else
{
gl_Position = vec4( −1000, −1000, 0, 0 );
}
v_lifetime = 1.0 − ( u_time / a_lifetime );
v_lifetime = clamp ( v_lifetime, 0.0, 1.0 );
gl_PointSize = ( v_lifetime * v_lifetime ) * 40.0;
}
The first input to the vertex shader is the uniform variable
u_time
. This
variable is set to the current elapsed time in seconds by the application.
The value is reset to 0.0 when the time exceeds the length of a single
