Real-Time Preview

Cycles 4D includes a real-time preview window so that, as you make changes to the scene, a preview image is automatically rendered. This makes changing lighting, materials, camera position etc. very easy to do since you can very quickly see the effect rather than having to render the scene.

Please be aware that at present there is a limit on the size of the output that can be rendered in the preview window. The preview will maintain the same image proportions as the full size render, but may be smaller if a large resolution is used. You can turn this off by unchecking 'Limit Render Size' in the window's 'Render' menu.

The reason for this is that otherwise you could select a very large output in the main render settings, try to preview it using the GPU, and get a crash with an out-of-memory error. Future versions of Cycles 4D may see this limit removed.

Using the Real-Time Preview

The preview is shown in a separate window. To open the window, got to the Cycles 4D menu then click 'Real-Time Preview'. This wall open the preview window and will render the current scene, giving something like this:

The size of the window is governed by the main Cinema render settings; the size of the preview is the same as the Width and Height settings in the Output section of the main render settings.

The render settings for the preview are the same as the Cycles 4D settings used for a full render.

Window controls

The following controls are available in the preview window:

This is a Pause button. Clicking this will prevent further automatic updating and the button will change to . Clicking it again will resume automatic updating and the button will change back to the 'pause' appearance.

If this button is clicked, a box with sizing handles will appear in the preview window. This is a render region (not the same as Cinema's render region) and when active only the area enclosed by this box will be rendered in the preview. To remove the box and render the whole window, click this button again.

Note that the preview must not be paused or clicking this button will have no effect.

This button is a toggle switch. Clicking it once will show the red component only of the image, and the button will display 'R' instead. Successive clicks will show the green, blue and alpha components before returning to the full RGB image.

Clicking this button will open the Picture Viewer window and send the preview image to it. Note that it does not render the scene to the Picture Viewer, it simply captures the current preview image and opens the Picture Viewer to display it.

This is the same as checking the Clay Material switch in the render settings. All objects in the scene will be rendered with a basic, light-grey diffuse material (a 'clay' material). However, this button only affects the real-time preview render. It has no effect on the final render to the picture viewer. Click the button again to restore the scene materials.

If you select this option, all materials in the scene are temporarily replaced by the clay material. If your scene is lit only by objects with an Emission shader, since those materials are replaced by the clay, the scene will go black because it no longer has any light. Just be aware of this if you do use this option.

Clicking this button will lock the currently selected camera. If you then change cameras in the object manager, the camera used for the real-time preview will not change. When a camera is locked, this icon will change to look like this:

If you click it again, then if no other camera is selected the camera will be unlocked. If a different camera is selected, that one will be locked instead.

Clicking this button will show the settings of the currently active camera in the attribute manager. You can then use the controls in the camera's object tab to select a focus object.


This is a simple zoom setting enabling you to zoom in and out of the preview image. You can also use the mouse scroll wheel in the image window to zoom, just as in the Picture Viewier.


Unlike the Zoom control, this changes the render resolution in the preview window. For example, suppose the render settings have an output size of (say) 1920 x 1200. This is a large size to render in the preview window, so you can reduce the size of the preview render by using this control. The value is a percentage of the output size, so if set to 50% the preview render will be half the width and height of the final render.

See also the 'Fit' command below.


This is the number of samples used for the preview render. This value is only used in the preview, so you can have a different value in the preview from the final output. This can be very useful to speed up the preview render if you have a high number of samples in the render settings.

Subd Rate

This is the subdivision rate used for micropolygon displacement. Its use is explained in the page How To: Use Displacement.

File menu

Save Image As...

This item enables you to save the image in the preview window to disk.


Clicking this item opens this manual.

Render menu

The first four entries in this menu correspond to a type of object to render in the preview - hair, motion blur, particles, and spline. Check or uncheck these entries to render (or not) the respective objects:

Limit Render Size

By default, Cycles 4D limits the size of the output that can be rendered in the preview window. The preview will maintain the same image proportions as the full size render, but may be smaller if a large resolution is used. You can turn the limit off by unchecking this menu entry.

Pause on Render

If this switch is checked and if the preview window is in the middle of updating a render, and you render the scene to the picture viewer, the real-time preview render will be paused until the main render is complete. This is to avoid the possible situation of two renders occurring simultaneously.


When checked, the rendered result from the real-time preview will also be shown in the viewport (note: the scene is not actually rendered to the viewport; instead, the rendered preview image is copied to the viewport). The real-time preview window must be open to show the preview render in the viewport, if the window is closed this feature will halt.


If you select this item, then whenever the real-time preview window is resized the render will be resized to fit the window. (This does not alter the render size in the main render settings.) Depending on the size of the preview window compared to the actual render proportions, non-rendering borders may be shown in the preview window. You can adjust the opacity of these borders in the main Cycles 4D preferences.

Resume Resends Data

If the render is paused and then resumed, the necessary data is sent to the render device again if anything has changed in the scene. but not if the scene hasn't changed. Very occasionally a situation can arise in which the data is not resent but should have been. If you encounter an error in the preview render which requires the RT preview render to restart from the beginning, turn this option on. This will force all render data to be resent and the render restarted.

Device menu

This menu contains a list of the devices available for rendering in the preview window. From here you can select which device Cycles 4D will use for rendering. The options depend on the devices you have installed but will always contain the CPU and either CUDA and/or OpenCL.

If you select CUDA or OpenCL as the render device, the menu is extended to include all the CUDA or OpenCL devices found on the system:

Then you can select which device to use for the preview window render. Note that this does not have to be the same device selected in the main Cycles 4D render settings, so you can render on different devices in the picture viewer and the real-time preview.

By default all CUDA or OpenCL devices are selected but you can turn one or more off to use only specific devices in the preview. If you uncheck all of them, the preview window will default to the CPU.

Note that the option in the main render settings to use the GPU plus the CPU is not available for the real-time preview.