The components communicate between each other using window properties and ClientMessages. These protocols can also be utilized by other clients to streamline their interaction with the window manager and to provide a better experience to the user.

When implementing new protocols, properties extending the data model of client windows are to be preffered over ClientMessages implementing actions.

Renderer

Implemented by: glass-renderer

Window rendering is implemented by the compositor, glass-renderer. It is controlled by properties both on individual client windows and on the root window.

Shader programs

Rendering is controlled by OpenGL shader programs. The programs must be specified on the root window, and can then be selected individually for each window.

Shader programs are responsible for drawing in two modes - normal visible mode, and a mode used for picking, where each pixel value corresponds to the window id and coordinates of that window.

Shader property mapping

All window properties are available to the shader code as uniforms. You must specify the right type as well as item count, e.g. vec4 MY_PROP corresponds to MY_PROP being of type XA_FLOAT and having 4 items. Windows and atoms are mapped to int. Uniforms for properties that are not set on a window, are set to 0 for integers, and NaN for floats.

Root window properties are available with the prefix root_, e.g. int root__NET_ACTIVE_WINDOW corresponds to the _NET_ACTIVE_WINDOW property on the root window.

Shader atom mapping

Atom values are also available as integer uniforms, so that properties of type atom can be compared to them, their names prefixed by atom_, e.g. int atom__NET_WM_STATE_MODAL for the atom _NET_WM_STATE_MODAL.

Complex property types

For some more complex types, the mapping is less straight forward, and a single property is mapped to a set of uniforms, all with a single name prefix.

All texture uniforms come with a corresponding int uniform with the suffix enabled that is set to 1 when the property is set on the window, and 0 otherwize.

WM_HINTS icons

WM_HINTS icons are mapped as two textures - one for the alpha channel, one for the color:

    uniform sampler2D WM_HINTS_icon;
    uniform sampler2D WM_HINTS_icon_mask;
    uniform int WM_HINTS_icon_enabled;
    uniform int WM_HINTS_icon_mask_enabled;

_NET_WM_ICON icons

_NET_WM_ICON icons are mapped to textures

    uniform sampler2D _NET_WM_ICON;
    uniform int _NET_WM_ICON_enabled;

IG_SVG

To be able to render an SVG at full resolution at any zoom level an SVG can not just be a texture - it would be too big when you zoom in enough. Instead, it comes as a texture and transformation vector to offset and scale the texture:

    uniform sampler2D IG_CONTENT;
    uniform vec4 IG_CONTENT_transform;

To render the texture correctly, you should do something like this

    mat4 transform_mat = transpose(mat4(
      1./IG_CONTENT_transform[2], 0., 0., -IG_CONTENT_transform[0]/IG_CONTENT_transform[2],
      0., 1./IG_CONTENT_transform[3], 0., -IG_CONTENT_transform[1]/IG_CONTENT_transform[3],
      0., 0., 1., 0.,
      0., 0., 0., 1.
    ));
    vec4 texture_coord = transform_mat * vec4(window_coord, 0, 1.);
    fragColor = texture(IG_CONTENT, texture_coord.xy).rgba;

IG_ITEM

Properties of type IG_ITEM should contain a single window reference (as if of type WINDOW). Whenever a property of this type is encountered while rendering a window (this includes properties inherited from the root window), this references window is rendered (recursing). During this recursive rendering, the properties of the parent window are available to the shader with a parent_ prefix, e.g. parent_IG_COORDS. The intention is to allow for rendering window decorations like buttons.

Window properties

• IG_SHADER ATOM - the shader to use to render this window.
• IG_COORDS FLOAT[4] - Coordinates for the window on the desktop. A client can change these to move and resize a window.
• IG_SIZE INTEGER[2] - horizontal and vertical resolution of the window in pixels. A client can change these to change the window resolution without automatically resizing the window. A ConfigureRequest however, changes both resolution and size (proportionally).
• IG_LAYER ATOM - the desktop layer to place this window in
• IG_CONTENT IG_SVG - svg xml source code for an image to render instead of the window. Note: This rendering will support infinite zoom.

ROOT properties

• IG_SHADERS ATOM[any] - a list of shader programs. Each program needs to be further specified with the next three properties
  • shader_GEOMETRY STRING - geometry shader source code
  • shader_VERTEX STRING - vertex shader source code
  • shader_FRAGMENT STRING fragment shader source code
• IG_VIEWS ATOM[any] - a list of layers to display. Each layer needs to be further specified with the next two properties
  • layer_LAYER ATOM - layer name to match on IG_LAYER on windows
  • layer_VIEW FLOAT[4] - left,bottom,width,height of layer viewport (zoom and pan)
• IG_ANIMATE WINDOW - event destination for animation events

The user should make sure to provide a shader called IG_SHADER_DEFAULT.

The user should make sure to provide a view called IG_VIEW_MENU matching the window LAYER IG_LAYER_MENU, with a viewport of 0,0,1,0.75 (or whatever aspect ration your screen is). This layer will be used to display override redirect windows, such as popup-menus.

If either width or height of a view is set to 0.0, it will be updated (by glass-renderer) with a value corresponding to the other one (typically set to 1.0) and the current screen aspect ratio.

Example root properties:

    IG_VIEWS=[IG_VIEW_DESKTOP, IG_VIEW_OVERLAY, IG_VIEW_MENU]

    IG_VIEW_MENU_VIEW=[0.0, 0.0, 1.0, 0.75]
    IG_VIEW_OVERLAY_VIEW=[0.0, 0.0, 1.0, 0.75]
    IG_VIEW_DESKTOP_VIEW=[0.0, 0.0, 1.0, 0.75]

    IG_VIEW_MENU_LAYER=IG_LAYER_MENU
    IG_VIEW_OVERLAY_LAYER=IG_LAYER_OVERLAY
    IG_VIEW_DESKTOP_LAYER=IG_LAYER_DESKTOP

Animator

Implemented by: glass-animator

Animations are implemented by glass-animator and controlled by setting window properties and sending ClientMessages.

To animate the value of the property prop from its current value to a new value, the property prop_ANIMATE should be set to the new value on the same window. The animation is then started by sending a ClientMessage with the following properties:

• window - The window pointed to by the IG_ANIMATE property of the root window
• type - IG_ANIMATE data[0] WINDOW - window with the property to animate data[1] ATOM - the property to animate, prop data[2] FLOAT - animation time in seconds

Coordinate systems

Windows have coordinates in the desktop (space) coordinate system, which is similar to the OpenGL one - x grows towards right, y upwards. Desktop coordinates have no natural units, as the desktop can be zoomed to any level, and there is nothing special about the 0 zoom level.

Window coordinates are for the top left corner of windows. Width and height are in the same units as x and y. Therefore, the coordinates occupied by a window ranges from ]x..x+w[,]y-h..y[.

About the FLOAT datatype

The FLOAT datatype is encoded as a 32 bit float stored in a 32 bit item in properties and events according to the normal 32 bit item rules of XGetWindowProperty etc - that is, it is stored on the X server in network byte order, and converted to/from local byte order by Xlib.

WARNING: On 64 bit platforms, XGetWindowProperty returns an array of long, which are 64, not 32 bits each. That means that the whole array CAN NOT be casted to an array of float, but each array item must be reinterpreted separately:

    float items[nr_items];
    XGetWindowProperty(
      display, window, property_name_atom, 0,
      sizeof(float)*nr_items, 0, AnyPropertyType,
      &type_return, &format_return, &nitems_return,
      &bytes_after_return, &prop_return);
    if (type_return != Success) return NULL;
    for (int i = 0; i < nr_items; i++) {
     items[i] = *(float *) (i + (long *) prop_return);
    }

Application ID:s

Implemented by: glass-annotator

The glass-annotator modifies the behavior of all applications.

At startup of an application any environment variables prefixed by either IG_APP_ or IG_GROUP_ are read and stored. Then environment of the application is modified, removing any IG_APP_ prefixed environment variables, so that they are not inherited by child applications. IG_GROUP_ ones are left unchanged. If an environment variable IG_APP_ID does not exist, a random value will be generated and used in its stead.

When ever the application opens a new window, all environment variables read at startup as per above, will be set as properties on the window. Additionally, the property WM_COMMAND will be set to the argv of the application.