[vert.glsl]
#version 120

attribute vec3 in_vertex;
attribute vec4 in_color;
attribute vec4 in_texcoord;

uniform mat4 in_model_view;
uniform mat3 in_normal_mat;
uniform mat4 in_proj;

varying vec4 pass_texcoord;
varying vec4 pass_color;

void main(void)
{
    vec4 vertex = in_model_view * vec4(in_vertex - vec3(0.0,0.5,0.0), 1.0);

    //Billboard calculations
    vertex.x += (1.0 * in_texcoord.z);
    vertex.y += (- 1.0 * in_texcoord.w);

    //pass datas
    pass_texcoord = in_texcoord;
    pass_color = in_color;

    gl_Position = in_proj * vertex;
}

[frag.glsl]
#version 120

#if defined GL_ES
precision highp float;
#endif

uniform sampler2D in_texture;

varying vec4 pass_texcoord;
varying vec4 pass_color;

const float cos_45      = 0.70710678118;
const float PI = 3.14159265358979323846264;

void main(void)
{
    vec4 color = texture2D(in_texture, pass_texcoord.xy);
    if (color.a < 0.01)
        discard;
    gl_FragColor = color * pass_color;
}