Sarah Clarity Studios

Chapter 2: Reach Envelopes & Sight Lines

Created by Sarah Choi (prompt writer using ChatGPT)

Reach Envelopes & Sight Lines for Prop Concept Artists

Reach envelopes and sight lines are the invisible geometry that governs how a player or character can approach, grab, actuate, and read a prop. Handles, triggers, latches, and displays live inside or outside those invisible volumes, and their legibility on camera determines whether intent is obvious or frustrating. This article translates human factors into depiction cues you can use during concepting and the production handoff, with emphasis on anthropometrics, grip geometry, and accessibility.

A reach envelope is the three‑dimensional volume a user can access without dangerous or exhausting postures. In neutral standing, it resembles a forward‑tilted half‑dome anchored at the shoulder; in seated or prone postures the dome flattens and becomes asymmetric due to arm rests, belts, or ground contact. Conceptually, think in layers: the primary envelope is comfortable with the upper arm near the torso and the wrist neutral; the secondary envelope extends by flexing the shoulder and leaning the torso; the tertiary envelope requires stepping, crouching, or twisting. When you place critical controls inside the primary envelope, the prop reads “easy to use.” When you push them to secondary or tertiary, it reads “deliberate” or “risky,” which can be used narratively for safeties, hatches, and high‑energy systems.

Anthropometrics makes those envelopes credible. Because hands and arms vary widely, anchor your designs to a sensible percentile band. A useful fiction band for games spans small adult to large adult, and you can bias toward gloves if your world implies PPE or hostile climates. For a handheld prop, sketch the shoulder pivot as an origin and build an arc to the intended grip center. The arc radius is forearm length plus hand length for a neutral elbow; add a second, larger arc for an outstretched elbow to represent secondary reach. For fixed installations like consoles, lockers, or valves on bulkheads, draw both arcs for characters of different sizes and note where their volumes overlap. That overlap zone is the “universal” placement region; positioning handles and UI there suggests good industrial design and reduces animation awkwardness.

Grip geometry refines where inside the envelope the hand prefers to land. A power grip thrives slightly below shoulder height and a little inside the body’s midline, where the wrist can stay straight under load. A precision pinch prefers near‑midline and slightly higher than elbow height to allow visual supervision and fine motor control. A pull handle that lives above shoulder height forces shoulder flexion and reads as strenuous; one far below knee height reads as maintenance‑only. Use these reads on purpose: a red safety dog that requires a high reach broadcasts seriousness, while a maintenance latch that hides low and inside an access cavity signals restricted use. In your drawings, ghost a simplified arm with three joints and show the wrist angle at contact. Neutral wrists and minimal ulnar deviation look effortless; severe bends look punishing.

Sight lines determine whether the player or character can understand what to do without guessing. The eye seeks edges, icons, and motion that align with the camera’s dominant angle. In first‑person, the prop fills the lower right or left quadrant; in third‑person and isometric views, props share the frame with bodies and environment. To make function read, align the actuation vector with the view vector when possible: a twist knob whose scallops face the camera, a pull handle with a visible lip, or a lever whose long axis foreshortens toward the viewer during action. If the control must face away, provide secondary cues that wrap around—index notches, color bands, or relief arrows that remain visible from oblique angles. Avoid relying solely on paint; build the instruction into silhouette so it survives grime, damage, and low light.

Lighting and reflectivity heavily affect sight lines. A glossy, dark control embedded in a glossy housing disappears at distance; a slightly different roughness or a micro‑bead texture separates the part by specular behavior without resorting to high saturation. Chamfers on leading edges create controlled edge highlights that survive compression and motion blur. If your world is low‑light or flicker‑lit, favor larger chamfers and proud features that catch grazing light. Conversely, high‑glare labs or medbays suggest anti‑glare textures and shaded recesses around displays; frame the display with a shallow well so it remains readable regardless of angle.

Clearance volumes are the cousins of reach envelopes. Once the hand reaches a control, it needs space to form a grip and to move through its range without knuckles colliding with guards, bezels, or neighboring props. For a knob, imagine a torus around the knob’s outer diameter equal to finger thickness; for levers, imagine a swept volume that includes the hand and wrist for the entire throw. In concept, draw these as translucent shapes; in production, annotate them as minimum keep‑outs so level dressing and animation never trap the hand against geometry. When you show a tight space on purpose—like a recessed arm‑safe reset—make the recess obviously oversized for a gloved finger if the fiction demands field service, or obviously undersized if you intend “tool‑only” access via a spanner or key.

Posture shifts move envelopes and sight lines in tandem. Crouching brings the eye line down and the primary reach inward; climbing or hanging extends it upward and forward while complicating wrist neutrality. Seated postures with harnesses, cockpits, or saddles restrict torso lean and bias reach toward midline. If your prop is cockpit‑mounted, prioritize controls within a forward horseshoe from thigh to shoulder height, and keep frequently toggled controls near the dominant hand’s natural fall. Ground‑mounted props like hatches or field lockers benefit from handles that sit just below elbow height in a half‑crouch, which reads usable for both small and large characters and telegraphs “shared tool.” Convey posture by sketching ground plane, pelvis tilt, and a quick ribcage block so reviewers can judge plausibility at a glance.

Camera discipline strengthens sight lines. Decide your target lens and distance early, because a wide FOV exaggerates perspective and hides small controls at the edges, while a tighter lens flattens forms and emphasizes silhouettes. If a control is narratively important, design it to survive your widest gameplay lens: amplify edge breaks, use bolder negative spaces, and avoid micro‑textures that alias. In keyframes and callouts, present at least one view from the expected gameplay angle and one orthographic with the control in full profile. That pairing allows both readability checks and mechanical clarity.

Environmental obstacles shrink envelopes. Armor plates, backpacks, capes, winglets, and weapon slings all steal reach in certain directions. A pauldron can prevent a shoulder from elevating; a bracer can collide with inward‑facing levers; a messenger bag can cover a hip‑mounted holster. Incorporate these constraints by sketching the character’s kit as blocking volumes before finalizing handle placement. For non‑humans or exo‑assisted characters, restate the envelope in their mechanics: a mech hand might have limited finger splay but excellent crush force; a tentacular manipulator has reach everywhere but poor precision near hard stops; a powered exo may extend reach but limit pronation/supination. Show how the control adapts: bigger paddles for mitt‑like grippers, indexed sockets for tentacles, or orthogonal toggle arrays for limited rotation.

Accessibility is the ethical and cinematic win. Build alternate paths to actuation so a user with reduced strength, smaller hands, or gloves can still succeed. A bail handle admits a hook grasp from odd angles; a T‑bar turns pinch into torque; a secondary tether point converts lift into pull. Keep high‑frequency controls in the primary envelope of both small and large users; push low‑frequency maintenance controls into secondary zones but ensure sight lines still hint at their existence. Where state must be read at a distance—armed/disarmed, locked/unlocked—encode state in form: proud versus flush, open versus closed gaps, rotated versus aligned tabs. For accessibility under stress, sync tactile changes with visual ones so a panicked user can verify by feel and by glance.

For handheld props, the envelope moves with the user, but relative sight lines matter. A magazine release that hides behind a finger swell will never read in a third‑person camera; an inset toggle on the spine of a device will collect grime and become invisible in backlit frames. Favor controls that break silhouette on at least one face, and provide an index so the hand finds orientation without looking. If the prop is used at arm’s length—flashlights, scanners, med‑injectors—place displays where they align with the natural eye line for the intended grip, typically just above thumb line and canted toward the face. If the narrative demands awkward reads, emphasize it honestly: rotate the display away and show secondary affordances like audio ticks or haptic coils so usability doesn’t vanish, only shifts modality.

Clarity in world scale is gained through consistent human references. Include a ghosted hand or a simple 95th‑percentile outline behind panels and consoles to prove reach claims. If you use measurement callouts, pair absolute dimensions with “from” and “to” anchors like shoulder pivot to grip center, or seat H‑point to console top, so rigging can reproduce the posture. For animation, indicate the pivot angle range for levers and the degrees per detent for rotaries; for level design, box out the clearance volumes so collision meshes don’t erase your usability.

Testing your assumptions is fast and cheap. Tape a rectangle on your wall to stand in for a console and mark likely control positions. Approach it from different postures and camera heights; note which positions feel natural, which require shoulder hiking, and which occlude from a camera placed at typical gameplay eye height. For handhelds, print a one‑to‑one silhouette and verify index placement with your own hands or with gloves. Photograph these tests next to your paintovers so reviewers understand that the placements are not arbitrary.

Sight line choreography is storytelling. Where the eye lands first should be where the hand belongs next. A strong edge highlight on the main handle leads to a secondary control tucked behind it; a bright specular on a safety collar resolves into a darker, grippier twist crown; a notch aligns with an icon that matches a sound cue when actuated. The sequence is a visual sentence: notice, reach, grip, confirm, act. When the sentence is smooth, the prop feels inevitable; when it is broken, the prop feels hostile or mysterious—useful if that is the point.

Production notes translate this invisible geometry into buildable guidance. Provide a plan view showing the primary and secondary reach arcs for your assumed user sizes, a side view with eye heights and sight rays to the main controls, and a section that illustrates clearance volumes through the full range of motion. Specify whether clearances assume bare hand or light/heavy glove. Define the intended camera angle and typical distance so surfacing and textures are scaled for the read. If a control is intentionally outside primary reach as a safety, label it as such and note the required posture so animation and combat systems can budget the time cost. If a display must remain readable from off‑axis, state the cant angle and any anti‑glare treatment implied by your materials.

Finally, tie reach envelopes and sight lines back to character and world. Elite operators and mechs might flaunt expanded envelopes through training or hardware, allowing tighter clusters of controls with steeper learning curves. Civilian infrastructure favors broad, forgiving envelopes with big, self‑explanatory sight lines. A clandestine device may hide its true control outside normal envelopes while leaving decoy affordances in plain sight. In each case, the invisible geometry becomes part of the prop’s voice, telling the player how close to get, where to look, and how to act before a single label is read.