VR Billboard Shader

This shader fixes VR billboard issues, keeping billboards properly aligned for a natural VR experience.

Add as shader material override to your sprite or mesh and it should work. 

Shader code

shader_type spatial;
render_mode unshaded, depth_draw_opaque, cull_disabled;

uniform sampler2D albedo_texture : source_color;

void vertex() {
    // Get the model position in world space
    vec3 model_pos = MODEL_MATRIX[3].xyz;

    // For VR, we'll use the eye position directly
    vec3 camera_pos = CAMERA_POSITION_WORLD;
    vec3 to_camera = normalize(camera_pos - model_pos);

    // Calculate the right vector
    vec3 right = normalize(cross(vec3(0.0, 1.0, 0.0), to_camera));
    // Keep up vector strictly vertical
    vec3 up = vec3(0.0, 1.0, 0.0);
    // Recalculate forward vector to ensure orthogonality
    vec3 forward = normalize(cross(right, up));

    // Build the billboard matrix
    mat4 billboard_matrix = mat4(
        vec4(right, 0.0),
        vec4(up, 0.0),
        vec4(forward, 0.0),
        vec4(model_pos, 1.0)
    );

    MODELVIEW_MATRIX = VIEW_MATRIX * billboard_matrix;
}

void fragment() {
    vec4 albedo = texture(albedo_texture, UV);
    ALBEDO = albedo.rgb;
    ALPHA = albedo.a;
    ALPHA_SCISSOR_THRESHOLD = 0.5;
}

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