Howler's drawing tool-set is shown as a series of icons on the Tool Panel. The tool panel may be 1 column or to, free floating, or it may be docked to the sidebar along the left or right side of the main window. The tool panel has functions for drawing, making selections, managing the view-state (panning and zooming) and clearing the image and undoing and re-doing changes made to it.

*Right clicking on most of the tools brings up a menu or option panel related to it.

*Selecting a tool on the toolbar changes the options on the context strip that is available across the top of the main window.

Drawing tools include the brush tool, the flood-fill tool (paint can,) the line and curve tools, and the rectangle and ellipse tools.

1. The natural paint tool activates the powerful natural media painting capabilities. See the section on Natural tools
   Selecting the natural paint tool displays a unique set of controls and settings associated with it on the context strip. Perhaps the most important option here is the “Browse media” button, which allows you to select from many different drawing media presets.

2. The rectangle tools draws a filled or unfilled shape. Depending on which part of the icons you click on, the rectangle and ellipse tools are filled or unfilled. There's a dividing line to show you. Right clicking on the icons brings up the fill settings/gradient panel. See the section on gradients for more information. The context strip for this
   tool gives you additional options for how to draw the inside and outline of the rectangle. A “Filled shape” checkbox determines if the rectangle is filled (with the current fill settings) or only the outline is drawn. (A shortcut is to click on the upper left/lower right portions of the rectangle tool)
   There are also options to draw the outline shape using the current natural media settings, or to use a more graphical rendering style, in which case, the shape can start or end with special “Caps” such as an arrow pointer or rounded shape.

3. The Ellipse tool, like the Rectangle tool, draws a filled or unfilled shape. The ellipse tool shares most of its context strip settings with the rectangle tool.
    

4. The paint can lets you flood fill areas that are surrounded by pixels.  Right click on it for more options, including the tolerance at which border detection happens.

The unfilled rectangle and ellipse tools, as well as the line and arc tools can be used with any of the natural medias. Just select the media you want, then select the drawing tool you want to draw it with.

The Selection tools, or alpha channel tools let you work with a mask. A mask, (or stencil) holds back part of your paint so can can paint on just certain areas of an image.

1. The lasso tool lets you ‘select’ part of an image for further exclusive manipulation. You may also pick up this selection and use it as a custom brush. Right clicking on this tool brings up the Alpha channels panel.
   
   
   

2. The Rectangle to alpha tools lets you draw a rectangle into the alpha channel. This can also be thought of as 'selecting' part of an image. Right clicking on this tool brings up the alpha channel panel.
   
   
   

3. The Ellipse to alpha tool lets you draw an ellipse shape into the alpha channel. Right clicking on this tool brings up the alpha channel panel.
   
   
   

4. The alpha magic wand tool lets you ‘select’ and area in your image based on its similarity to the pixel you select.

Next up are the Brush Selector tool, the FX tool, the Curve tool, and the Text tool.

*The Custom Brush tool lets you pick up a portion of an image to use as a new painting tool or to place it in another location.

*Note the many uses of the FX tool

1. The custom brush selector lets you pick up a portion of your image and use it as a brush. Right clicking on this tool brings up the brush keyer panel. With the brush keyer panel, you can make areas of the brush transparent. See the section on Custom brushes.
   
   
   

2. The linear tools basic function is drawing lines. However, right clicking on this tool lets you select from a number of functions including Linear gradient, Circular gradient, Warp, Linear alpha fader, Nova, Lens flares, and Lightning. See Linear tools.
   
   
   

3. The arc tool lets you draw arcs with the current media.
   
   
   

4. The text tool lets you place a line of text into your image. Right clicking on this tool brings up a menu of options.

Navigation tools

These tools are complemented by the keyboard shortcut (CTRL+Shift) for dynamically panning and zooming around in your image.

1. The Hand tool lets you pan around in your image to reveal more of it if you are zoomed in. It does not force you to switch tools. Just scrolling around on the icon will scroll the image. Using the keyboard shortcuts (CTRL+Shift) will have the same effect when you scroll around in the image's window. Doing the same with the Right Mouse Button will zoom in and out.
   
   
   

2. The Zoom tool lets you zoom in and out. You don't need to move your cursor over the image. It will be placed in the center automatically, as a shortcut.
   
   
   

3. This icon will pop your zoom level back to 100% (1 to 1 pixel ratio)
   
   
   

4. This icon will scale your display so the whole image will fit on screen with no hidden areas.

1. The Turkey baster (aka eye-dropper) tool lets you pick up a color from your image. Right clicking lets you specify how large of an area to sample.
   
   
   

2. The undo tool undoes the last painting operation. Right clicking redoes the last undone operation. Middle clicking and dragging lets you interactively fade the last painting operation.
   
   
   

3. The clear button clears the image to the current secondary color. Right clicking brings up a panel of options for clearing your image or current selection. You can also clear an entire animation from here.

Brush settings

The context strip for the natural media tool holds many common parameters for controlling your brushes.

There are many more on the brush settings panel.

The “Prv” button let's you see a preview of a custom brush before you stamp it down. This is only effective for custom brushes, and not internal brushes or the anti-aliased pen.

The next two buttons allow a digitizing tablet (such as a Wacom tablet) pressure to control the size and opacity of your brush.

Size controls the size of most brushes. If a brush is a custom brush, the 'Allow brush transforms" has to be ticked on the brush settings panel, or the “Tr” button on the context strip for brushes. Sometimes you want a custom brush that can be sized just like other brushes, and sometimes you want to use a custom brush for other operations, such as copying images around on the screen, in which case you may not want the brush to be arbitrarily scaled.

Opacity controls how opaque (or transparent) a brush is when you draw with it. When stamping a brush down, the effect will build up over time, making it more opaque.

Step controls the spacing between brush 'stamps'

Selecting a mode will determine how the brush is applied when you draw. See the section on paint modes for examples.

Speed scale causes the speed of the mouse or pointing device to effect the scale of the brush. This can be a good way to allow some pressure-like effects without a pressure enabled device, but it can also be confusing and difficult to control, so use as you see fit. Some presets in the Media Browser have this option enabled, and if you find it difficult, you can turn this option off and re-save the effects, or use other presets.

Random Position (Rand pos) causes the brush to be stamped down in random positions, relative to the brush stroke.

Random Size (Rand size) causes the brush to randomly scale, relative to the current brush size.

Random angle causes the brush to be rotated randomly, relative to the current brush angle and tilt (from a digitizing device, if any)

Rand Hue causes the brush to be rendered with the hue (color component) of the brush altered randomly.

Rand Saturation causes the brush to be rendered with the saturation (amount of color intensity) of the brush altered randomly.

Rand Value causes the brush to be rendered with the value (brightness or luminance) of the brush altered randomly.

Bleed causes the brush to pick up a small amount of the underlying color as it is being painted, and blend it with the painting color. Very high values give the best results for this setting.

Dryout causes the brush to loose opacity over time, simulating the effect of a brush running dry or out of pigment over time.

Rel step (Relative step) causes the step value to be relative to the size of the brush stamp instead of absolute pixels. With Rel step enabled, a step value of 100 means that the brush will be rendered when the pointing device moves the equivalent of the size of the current brush image.

Drawing modes are accessed from the context strip, or from the brush settings panel.

Default mode uses a straight copy of the paint color, effectively replacing one color with the other. It has the effect of looking like an opaque paint like gouache.  Paper texture, opacity, and other brush settings also have an effect on the final color.

Additive mode Adds the red, green, and blue values of the paint color to the color in the image. For example, if you paint with blue onto a red image, you would get a bright purple color.

Subtractive mode subtracts the paint color from the color on your image.  Here, red is the color being subtracted.  It appears as cyan over the white area because it is white - red.  The yellow area shows up as green because it is yellow - red.

Multiply mode multiplies the paint and image colors.  The result is never brighter than the original values. This mode is similar to painting with translucent ink, and can be used for watercolor effects.  It is also highly useful for combining images or textures together.

Divide is the complement of multiply. Use it as you see fit.

Screen is similar to additive, but it keeps an image from ‘blowing out’ or becoming overly bright. It’s often useful for effects like stars and fire.

Around gray combines two colors around their middle brightness level.  It is useful in cases where your background is grey, and you want to make it either lighter or darker, depending on the color in the brush.

Rub-through mode lets you paint, or rub, one image onto another. The source of the image is the swap image. To copy an image into the swap image, press 'J' (capital j) on the keyboard.  You can turn on layer mixing from the layers panel to see both layers at the same time, then paint one onto the other.  In the example, a photograph has been rubbed into a gray image with an airbrush tool.

Panto mode (Pantograph) lets you copy part of an image from one area of your image to another. Shift click to set the source area. This effect is used quite often in image touch-ups to remove blemishes and errors from an image.  In the example, the tree has been cloned.

Smear, as it implies lets you smear an image. Changing the opacity, steps, and the brush shape itself has a tremendous impact on the actual effect achieved.

Paint-smear mode is a combination of default mode and smear mode. The initial stamp of paint is done in default mode, and it is then switched to smear mode. The result is like painting with oil paints.

Pattern uses the current custom brush as a pattern. Generally, you select an area of the image as a custom brush and then switch to one of the internal brushes to paint.  Currently, painting with a custom brush in pattern mode will use the same brush as the pattern.

Offset pattern randomly changes the position of your patter by a small amount every time you make a brush stroke. This is useful for giving an image an impressionist style, or for creating textures that do not repeat at regular intervals.

The sidebar

The side-bar in Howler is the place where many of the program's tools and settings reside.

Panels on the sidebar are hidden or revealed (telescoped) by clicking on their caption (or tab)

When expanded, the “+” on the caption area will turn into a “-” indicating that this panel can be minimized.

If the sidebar uses up to much of your screen space, or you just want more space for painting, the sidebar can be collapsed out of the way at any time by clicking the thumb-tab on the side of the side-bar

The Previews tab on the sidebar

This first panel on the sidebar shows the Current brush preview, the current paper preview, and the current image preview.

1. The current brush preview. This shows you the currently selected brush image. Left clicking on this image brings up the brush options panel. Right clicking brings up a set of built in brush images.

2. Right clicking the center thumbnail brings up the Paper panel, and Left clicking it toggles the current setting for the paper effect.

   The image preview shows a small image of the current image you are working on. Right clicking on this image brings up a menu of options for working with images.
   

The Compact tab on the sidebar

The compact tab on the sidebar gives you a very small color mixer, for such cases when screen space is limited, or you need more space for other tabs on the sidebar to be open. The arrow on the right side allows you to alter the saturation of the compact color picker. See the section on color for more information.

The Color Picker on the sidebar

The color picker tab on the sidebar gives you 7 different tools for selecting colors from various color models.

The option dropdown control gives you a lot of other tools and options for controlling color. See the section on color for more information.

The Color Swatch on the sidebar

It is often helpful, if not critical, for a computer artist to work from a limited number of colors. The color swatch (also known as wells) on the sidebar is a place where you can keep often used colors or color-schemes.

Color swatches can be built by the user and stored for later use. The arrows at the bottom lets you cycle through previously saved color wells.

See the section on color to learn how to build custom color wells, and for more information.

The Layers panel on the sidebar

Layer mixing allows you to create an image from separate layers. The layers can be combined in many different ways.

See the section on layer mixing for more information.

The Info panel on the sidebar

The info panel on the sidebar gives you a lot of information about your current painting session, such as your current paint and brush modes.

Perhaps most importantly, you can view your current pixel coordinates, and the color of the pixel under your pointer. This can be viewed in RGB color, or in hexadecimal (web friendly) format.

You can also tell from here if GPU support is enabled. The GPU is a hardware processor in your computer that can be used to accelerate a number of functions inside of Howler.

Grid settings on the sidebar

The grid settings panel on the sidebar gives you control over your rulers and grid settings. Most of these settings are remembered when you leave the program.

For more information, see the section on Display Settings.