storm 0.11.0

A personal 2D game engine designed for performance
Documentation 
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precision highp float;

const float TWO_PI = 6.283185307179586476925286766559;

layout(location = 0) in vec3 a_pos;
layout(location = 1) in vec2 a_size;
layout(location = 2) in vec4 a_uv;
layout(location = 3) in vec4 a_color;
layout(location = 4) in float a_rotation;

out vec2 v_uv;
out vec4 v_color;

layout(std140) uniform vertex {
    mat4 ortho;
};

// UV Layout: xmin xmax ymin ymax
// ymin and ymax are swapped below because OpenGL reads images from bottom row to top row, but
// they're stored top to bottom on upload, so this corrects that.
vec4 uv_lut[4] = vec4[4](
    vec4(1.0, 0.0, 1.0, 0.0),  // left bottom
    vec4(1.0, 0.0, 0.0, 1.0),  // left top
    vec4(0.0, 1.0, 1.0, 0.0),  // right bottom
    vec4(0.0, 1.0, 0.0, 1.0)); // right top

vec2 size_lut[4] = vec2[4](
    vec2(0.0, 1.0),  // left top
    vec2(0.0, 0.0),  // right top
    vec2(1.0, 1.0),  // left bottom
    vec2(1.0, 0.0)); // right bottom

vec4 rotateZ(vec3 pos) {
    float psi = TWO_PI * a_rotation;
    float sina = sin(psi);
    float cosa = cos(psi);
    vec2 origin = vec2(
        a_pos.x + (a_size.x * 0.5),
        a_pos.y + (a_size.y * 0.5));
    return vec4(
        (cosa * (pos.x - origin.x)) - (sina * (pos.y - origin.y)) + origin.x,
        (sina * (pos.x - origin.x)) + (cosa * (pos.y - origin.y)) + origin.y,
        pos.z,
        1.0);
}

void main() {
    vec4 temp = a_uv * uv_lut[gl_VertexID];
    v_uv = vec2(temp.x + temp.y, temp.z + temp.w);
    v_color = a_color;

    vec3 size = vec3(a_size * size_lut[gl_VertexID], 0.0);
    vec3 pos = a_pos + size;
    gl_Position = ortho * rotateZ(pos);
}