COMPUTER GRAPHICS

CS 482 – FALL 2014 OCTOBER 6, 2014 TEXTURE MAPPING

• • • • TEXTURES BUMP MAPPING ENVIRONMENT MAPPING PROCEDURAL TEXTURING

TEXTURES BASICS

MAPPING A PATTERN ONTO THE OBJECTS’ SURFACES CAN GREATLY ENHANCE THE SCENE’S APPEAL AND/OR REALISM.

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TEXTURES UV COORDINATES

ONE APPROACH TO TEXTURE MAPPING DIRECTLY MAPS THE 2D TEXTURE COORDINATES (CALLED

UV SPACE

) INTO THE 3D WORLD SPACE COORDINATES.

PLANAR MAPPING CYLINDRICAL MAPPING SPHERICAL MAPPING CS 482 – FALL 2014 OCTOBER 6, 2014: TEXTURE MAPPING PAGE 150

TEXTURES TILING

WHEN THE SURFACE BEING TEXTURED IS MUCH LARGER THAN THE IMAGE BEING MAPPED, IT IS POSSIBLE TO TILE THE IMAGE REPEATEDLY OVER THE SURFACE.

CARE MUST BE TAKEN TO DEVELOP IMAGES THAT DO NOT PRODUCE DISCERNIBLE SEAMS OR PATTERNS WHEN TILED.

THE SEAMS AND PATTERNS ARE MORE NOTICEABLE IN THE TILED HEDGE IMAGE ON THE LEFT THAN THE ONE ON THE RIGHT.

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BUMP MAPPING ADJUSTING NORMAL VECTORS

TO ADD MORE REALISM TO A TEXTURE-MAPPED IMAGE, AN ADDITIONAL ACTION, KNOWN AS A BUMP MAPPING, CAN BE APPLIED TO THE OBJECT’S SURFACE.

APPLYING THE TEXTURE TO THIS SURFACE, WHILE COMPUTATIONALLY EXPENSIVE, PRODUCES A SENSE OF DEPTH FAR SUPERIOR TO SIMPLE TEXTURE MAPPING.

BUMP MAPPING (LEFT) ALTERS THE SURFACE’S NORMAL VECTOR, WHILE DISPLACEMENT MAPPING (RIGHT) ALTERS THE SURFACE ITSELF.

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BUMP MAPPING INTACT SILHOUETTE

BUMP MAPPING BASICALLY APPLIES A PATTERN OF PERTURBATIONS TO THE NORMAL VECTORS ON THE SURFACE OF THE OBJECT BEING RENDERED.

 = CS 482 – FALL 2014 WHEN AN ILLUMINATION MODEL (E.G., PHONG SHADING) IS APPLIED WITH THESE ALTERED NORMAL VECTORS, THE APPEARANCE OF A RICH, DETAILED TEXTURE RESULTS.

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BUMP MAPPING DISPLACEMENT MAPPING

DISPLACEMENT MAPPING, WHICH ACTUALLY ALTERS THE OBJECT’S UNDERLYING GRID TO IMPLEMENT THE 3D SURFACE DETAILS, ELIMINATING THE SILHOUETTE INCONSISTENCIES, BUT GREATLY INCREASING THE PROCESSING COST.

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ENVIRONMENT MAPPING SPHERICAL MAPPING

TO PRODUCE AN EFFECT THAT APPEARS LIKE 3D REFLECTION, ENVIRONMENT MAPPING PROJECTS THE SURROUNDING ENVIRONMENT ONTO A 2D IMAGE AND THEN TEXTURE MAPS THAT RESULT ONTO THE “REFLECTIVE” OBJECT.

WITH SPHERICAL MAPPING, THE ENTIRE ENVIRONMENT IS MAPPED TO A RADIUS ONE DISK (THE FRONT TO THE INNER CORE OF THE DISK AND THE REAR TO THE OUTER RING).

CROSS-SECTION OF ENVIRONMENT, WITH FRONT ON THE RIGHT AND REAR ON THE LEFT CS 482 – FALL 2014 BAD NEWS: THE ENTIRE PERIMETER OF THE SPHERE MAP IS MAPPED TO A “SINGULARITY” ON THE FAR SIDE OF THE OBJECT.

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ENVIRONMENT MAPPING LATITUDE MAPPING

WITH LATITUDE MAPPING, THE SPHERE IS TREATED LIKE A GLOBE AND MAPPED FROM 3D TO 2D VIA LONGITUDES AND LATITUDES.

BAD NEWS: THERE IS STILL A SEAM WHERE THE LEFT AND RIGHT EDGES OF THE TEXTURE MAP MEET WHEN MAPPED TO THE OBJECT.

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ENVIRONMENT MAPPING CUBE MAPPING

IN CUBE MAPPING, SIX TEXTURES ARE CREATED FROM EACH POSITIVE AND NEGATIVE CARTESIAN DIRECTION SURROUNDING THE OBJECT.

BAD NEWS: PARTICULAR FACETS OF THE OBJECT MIGHT REQUIRE UP TO THREE RENDERINGS (E.G., FRONT, RIGHT, AND BOTTOM) TO ENSURE THAT ALL FACES HIT BY THE REFLECTION RAYS ARE DISPLAYED.

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PROCEDURAL TEXTURING PERLIN NOISE

CERTAIN TEXTURES IN NATURE (CLOUDS, MARBLE, STREAMS, ETC.) TEND TO FOLLOW A PSEUDORANDOM PATTERN THAT MAY BE SIMULATED BY MEANS OF NOISE FUNCTIONS.

A SET OF PSEUDORANDOM VALUES ARE GENERATED AT SET INTERVALS.

A CONTINUOUS CURVE IS GENERATED BY SMOOTHLY INTERPOLATING BETWEEN THESE INTERVAL GAP).

VALUES.

SEVERAL CURVES LIKE THIS ARE GENERATED, EACH WITH CERTAIN RESTRICTIONS ON THE AMPLITUDE (THE DIFFERENCE BETWEEN THE MINIMUM AND MAXIMUM VALUES GENERATED) AND THE WAVELENGTH (THE SUMMING THESE CURVES YIELDS THE FINAL NOISE FUNCTION.

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PROCEDURAL TEXTURING NOISE TEXTURES

EXTENDING THE GENERATING OF A NOISE FUNCTION TO TWO DIMENSIONS YIELDS INTERESTING AND USEFUL TEXTURES.

+ + + + + = CS 482 – FALL 2014 OCTOBER 6, 2014: TEXTURE MAPPING PAGE 159

PROCEDURAL TEXTURING TEXTURE SYNTHESIS

TO SYNTHESIZE A LARGER IMAGE THAT FOLLOWS THE SAME PATTERN AS A GIVEN SMALLER IMAGE, START WITH A NOISY IMAGE OF THE DESIRED SIZE.

REPLACE EACH PIXEL IN THE NEW IMAGE BY LOOKING AT ITS ALREADY COLORED NEIGHBORS, FINDING A PIXEL IN THE ORIGINAL IMAGE WITH THE CLOSEST PATTERN OF NEIGHBORS, AND COLORING THE NEW PIXEL WITH THAT OLD PIXEL’S COLOR.

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