parallaxMapping.glsllib

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// Copyright (C) 2023 The Qt Company Ltd.

// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only

vec2 qt_parallaxMapping(in vec2 uv,

                        in sampler2D heightMap,

                        in vec3 tangent,

                        in vec3 binormal,

                        in vec3 normal,

                        in vec3 vertex,

                        in vec3 cameraPosition,

                        in float depthScale,

                        in float minLayers,

                        in float maxLayers)

    mat3 tanFrame = transpose(mat3(tangent, binormal, normal));

    vec3 viewDir = normalize(tanFrame * vertex - tanFrame * cameraPosition);

    float numLayers = mix(float(maxLayers), float(minLayers), abs(dot(vec3(0.0, 0.0, 1.0), viewDir)));

    float layerDepth = 1.0 / numLayers;

    float currentLayerDepth = 0.0;

    vec2 P = viewDir.xy * depthScale;

    vec2 delta = P / numLayers;

    vec2 offset = uv;

    float depth = textureLod(heightMap, offset, 0.0).r;

    float currentDepth = 0.0;

    while (currentDepth < depth)

        offset -= delta;

        depth = textureLod(heightMap, offset, 0.0).r;

        currentDepth += layerDepth;

    vec2 prevOffset = offset + delta;

    float afterDepth = depth - currentDepth;

    float beforeDepth = textureLod(heightMap, prevOffset, 0.0).r - currentDepth + layerDepth;

    float weight = afterDepth / (afterDepth - beforeDepth);

    return mix(offset, prevOffset, weight);