Reference Render viewer pane

This is a new feature in Houdini 10. To learn about more new features, see what’s new in Houdini 10.

The Render viewer pane renders the scene and can automatically preview changes quickly as you edit parameters.

This pane’s viewing interface is nearly identical to the standard image viewer , except that the render viewer cannot show multiple viewports at once. See how to use the image viewer for information on how to work with images in the render viewer.

Tasks

To...	Do this
Only update a sub-region of the image	Hold ⇧ Shift and drag a box around the area you want to render. The render view will only update this area. Shift-click without dragging to clear the region.
Save the current image to the image history	Click the snapshot button in the render history toolbar at the bottom of the render view. To give the image a unique name in history, enter it in the text box to the right of the snapshot button before you click it.
Inspect a pixel in the rendered image	Ctrl-click the pixel in the render view. By default, Houdini will print information about the pixel and open the associated object’s shader palette. You can override this behavior by overriding the “pick pixel” script .
Review saved images in the render history	Use the slider in the render history toolbar at the bottom of the render view. Alternatively, you can choose an image by name in the pop-up at the left end of the toolbar, or click the previous and next buttons to move through the image history. To delete an image from the history, go to an image in the history and click the Remove button next to the pop-up menu.
Compare the current image to an image from the render history	Right-click the Comparison method button near the right end of the toolbar and choose the image to compare to from the bottom of the menu. Right-click the Comparison method button again and choose a method for comparing the images, for example Split horizontal. Use the slider to control the comparison.

Render controls toolbar

Render	Regenerates shadow maps and renders the scene again. Any time you move a light that uses shadow maps, or change the geometry, click Render to recompute depth and shadow maps. This is disabled if you have not selected an output node to render.
	Restarts the current render. This will usually have no effect other than to recreate the exact same image.
	Pauses rendering. Click again to resume.
	Stops rendering the scene. This is disabled if the view is not currently rendering.
Output node pop-up menu	Choose the output node you want to render.
	Opens a floating parameter editor for the output node.
Preview checkbox	When this option is on, the view will show progressively more detailed previews of the scene as it renders. This makes the final output take a little longer but lets you get a sense of what the image will look like much faster. You will want this option on when Auto-update is on.
Auto-update checkbox	When this option is on, any parameter changes make the render view re-render. This lets you make changes in a node’s parameter interface and see the results in the render view interactively. If you turn this option off, use the Render button at the left end of the toolbar when you want to update the render view manually.
Preview method	“Blur” shows large anti-aliased pixels that are refined in each pass. “Sharp” shows a grainy, aliased image that becomes less grainy in each pass.
Update time	Time (in seconds) between preview passes. Mantra estimates the number of shading samples to use for the preview based on the speed of previous previews. So, if you have a faster machine, mantra will use more shading samples to generate a better preview in the given time.
Delay	Time (in seconds) between a parameter change and the auto-update. Increasing this time lets you combine small parameter changes when updating is slow.
	Opens this help page.

Render history toolbar

This toolbar lets you keep a history of rendered images from the render view. This is useful when you are playing with a parameter and want to compare the variations.

Pop-up menu	The pop-up menu at the left end of the toolbar controls which image is shown in the render view. Choose “Active Render” to show the active rendered image, or choose an image from the render history.
	Delete the currently shown image from the render history. This button is disabled when the pop-up menu is set to “Active Render”.
Slider	Use the slider or click the previous and next buttons to move through the history of saved images.
	Save the active rendered image to the render history. To give the image a unique name in the history list, enter it in the text box to the right of the button before you click it.
Comparison method button	Right-click the button to choose a comparison method. Click the button to turn comparison on or off.
Compare to menu	Click to choose the image to compare the current image to.
Comparison slider	Use the slider to control the comparison. This is disabled when the Comparison method pop-up menu is set to Off.

Add custom functionality to the render viewer

Use the iprview command to set the options of an IPR viewer pane.

Tip

The iprquery and iprquerys expression functions let you query information about the rendered image, such as which shader contributed the pixel at the given coordinates. These functions can be very useful for creating custom scripts.

Pick pixel script

When you Ctrl-click in the viewer, Houdini runs the script path/ipr/pickpixel.cmd script. By default, Houdini prints information about the pixel that was picked. If the pixel has a corresponding object, Houdini will open the shader palette for that object’s SHOP.

You can override the default behavior by inserting your own script earlier in the HOUDINI_PATH. Houdini calls the script with three arguments:

The name of the pane where you clicked.
X coordinate of clicked pixel.
Y coordinate of clicked pixel.

Drag and drop script

When you drag an operator onto the viewer, Houdini runs the script path/ipr/dragdrop.cmd script. You can override the default behavior by inserting your own script earlier in the HOUDINI_PATH. Houdini calls the script with five arguments:

The name of the pane where you dropped a node.
X coordinate of the drop.
Y coordinate of the drop.
The type of object dropped:
The name of the dropped object.