Graphics Reference
In-Depth Information
Example 14-11
Particle Rendering Vertex Shader
#version 300 es
#define ATTRIBUTE_POSITION 0
#define ATTRIBUTE_VELOCITY 1
#define ATTRIBUTE_SIZE 2
#define ATTRIBUTE_CURTIME 3
#define ATTRIBUTE_LIFETIME 4
layout(location = ATTRIBUTE_POSITION) in vec2 a_position;
layout(location = ATTRIBUTE_VELOCITY) in vec2 a_velocity;
layout(location = ATTRIBUTE_SIZE) in float a_size;
layout(location = ATTRIBUTE_CURTIME) in float a_curtime;
layout(location = ATTRIBUTE_LIFETIME) in float a_lifetime;
uniform float u_time;
uniform vec2 u_acceleration;
void main()
{
float deltaTime = u_time − a_curtime;
if ( deltaTime <= a_lifetime )
{
vec2 velocity = a_velocity + deltaTime * u_acceleration;
vec2 position = a_position + deltaTime * velocity;
gl_Position = vec4( position, 0.0, 1.0 );
gl_PointSize = a_size * ( 1.0 − deltaTime / a_lifetime );
}
else
{
gl_Position = vec4( −1000, −1000, 0, 0 );
gl_PointSize = 0.0;
}
}
This vertex shader uses the transform feedback outputs as input variables.
The current age of each particle is computed based on the timestamp that
was stored at particle creation for each particle in the
a_curtime
attribute.
The particle's velocity and position are updated based on this time.
Additionally, the size of the particle is attenuated over the particle's life.
This example has demonstrated how to generate and render a particle
system entirely on the GPU. While the particle emitter and rendering were
relatively simple here, the same basic model can be used to create more
complex particle systems with more involved physics and properties. The
primary takeaway message is that transform feedback allows us to generate
new vertex data on the GPU without the need for any CPU code. This
powerful feature can be used for many algorithms that require generating
vertex data on the GPU.
