android_frameworks_base/libs/hwui/ShadowTessellator.cpp

/*
 * Copyright (C) 2013 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <math.h>
#include <utils/Log.h>
#include <utils/MathUtils.h>
#include <utils/Trace.h>

#include "AmbientShadow.h"
#include "Properties.h"
#include "ShadowTessellator.h"
#include "SpotShadow.h"
#include "Vector.h"

namespace android {
namespace uirenderer {

void ShadowTessellator::tessellateAmbientShadow(bool isCasterOpaque, const Vector3* casterPolygon,
                                                int casterVertexCount, const Vector3& centroid3d,
                                                const Rect& casterBounds, const Rect& localClip,
                                                float maxZ, VertexBuffer& shadowVertexBuffer) {
    ATRACE_CALL();

    // A bunch of parameters to tweak the shadow.
    // TODO: Allow some of these changable by debug settings or APIs.
    float heightFactor = 1.0f / 128;
    const float geomFactor = 64;

    if (CC_UNLIKELY(Properties::overrideAmbientRatio > 0.0f)) {
        heightFactor *= Properties::overrideAmbientRatio;
    }

    Rect ambientShadowBounds(casterBounds);
    ambientShadowBounds.outset(maxZ * geomFactor * heightFactor);

    if (!localClip.intersects(ambientShadowBounds)) {
#if DEBUG_SHADOW
        ALOGD("Ambient shadow is out of clip rect!");
#endif
        return;
    }

    AmbientShadow::createAmbientShadow(isCasterOpaque, casterPolygon, casterVertexCount, centroid3d,
                                       heightFactor, geomFactor, shadowVertexBuffer);
}

void ShadowTessellator::tessellateSpotShadow(bool isCasterOpaque, const Vector3* casterPolygon,
                                             int casterVertexCount, const Vector3& casterCentroid,
                                             const mat4& receiverTransform,
                                             const Vector3& lightCenter, int lightRadius,
                                             const Rect& casterBounds, const Rect& localClip,
                                             VertexBuffer& shadowVertexBuffer) {
    ATRACE_CALL();

    Vector3 adjustedLightCenter(lightCenter);
    if (CC_UNLIKELY(Properties::overrideLightPosY > 0)) {
        adjustedLightCenter.y = -Properties::overrideLightPosY;  // negated since this shifts up
    }
    if (CC_UNLIKELY(Properties::overrideLightPosZ > 0)) {
        adjustedLightCenter.z = Properties::overrideLightPosZ;
    }

#if DEBUG_SHADOW
    ALOGD("light center %f %f %f %d", adjustedLightCenter.x, adjustedLightCenter.y,
          adjustedLightCenter.z, lightRadius);
#endif
    if (isnan(adjustedLightCenter.x) || isnan(adjustedLightCenter.y) ||
        isnan(adjustedLightCenter.z)) {
        return;
    }

    // light position (because it's in local space) needs to compensate for receiver transform
    // TODO: should apply to light orientation, not just position
    Matrix4 reverseReceiverTransform;
    reverseReceiverTransform.loadInverse(receiverTransform);
    reverseReceiverTransform.mapPoint3d(adjustedLightCenter);

    if (CC_UNLIKELY(Properties::overrideLightRadius > 0)) {
        lightRadius = Properties::overrideLightRadius;
    }

    // Now light and caster are both in local space, we will check whether
    // the shadow is within the clip area.
    Rect lightRect = Rect(adjustedLightCenter.x - lightRadius, adjustedLightCenter.y - lightRadius,
                          adjustedLightCenter.x + lightRadius, adjustedLightCenter.y + lightRadius);
    lightRect.unionWith(localClip);
    if (!lightRect.intersects(casterBounds)) {
#if DEBUG_SHADOW
        ALOGD("Spot shadow is out of clip rect!");
#endif
        return;
    }

    SpotShadow::createSpotShadow(isCasterOpaque, adjustedLightCenter, lightRadius, casterPolygon,
                                 casterVertexCount, casterCentroid, shadowVertexBuffer);

#if DEBUG_SHADOW
    if (shadowVertexBuffer.getVertexCount() <= 0) {
        ALOGD("Spot shadow generation failed %d", shadowVertexBuffer.getVertexCount());
    }
#endif
}

/**
 * Calculate the centroid of a 2d polygon.
 *
 * @param poly The polygon, which is represented in a Vector2 array.
 * @param polyLength The length of the polygon in terms of number of vertices.
 * @return the centroid of the polygon.
 */
Vector2 ShadowTessellator::centroid2d(const Vector2* poly, int polyLength) {
    double sumx = 0;
    double sumy = 0;
    int p1 = polyLength - 1;
    double area = 0;
    for (int p2 = 0; p2 < polyLength; p2++) {
        double x1 = poly[p1].x;
        double y1 = poly[p1].y;
        double x2 = poly[p2].x;
        double y2 = poly[p2].y;
        double a = (x1 * y2 - x2 * y1);
        sumx += (x1 + x2) * a;
        sumy += (y1 + y2) * a;
        area += a;
        p1 = p2;
    }

    Vector2 centroid = poly[0];
    if (area != 0) {
        centroid = (Vector2){static_cast<float>(sumx / (3 * area)),
                             static_cast<float>(sumy / (3 * area))};
    } else {
        ALOGW("Area is 0 while computing centroid!");
    }
    return centroid;
}

// Make sure p1 -> p2 is going CW around the poly.
Vector2 ShadowTessellator::calculateNormal(const Vector2& p1, const Vector2& p2) {
    Vector2 result = p2 - p1;
    if (result.x != 0 || result.y != 0) {
        result.normalize();
        // Calculate the normal , which is CCW 90 rotate to the delta.
        float tempy = result.y;
        result.y = result.x;
        result.x = -tempy;
    }
    return result;
}

int ShadowTessellator::getExtraVertexNumber(const Vector2& vector1, const Vector2& vector2,
                                            float divisor) {
    // When there is no distance difference, there is no need for extra vertices.
    if (vector1.lengthSquared() == 0 || vector2.lengthSquared() == 0) {
        return 0;
    }
    // The formula is :
    // extraNumber = floor(acos(dot(n1, n2)) / (M_PI / EXTRA_VERTEX_PER_PI))
    // The value ranges for each step are:
    // dot( ) --- [-1, 1]
    // acos( )     --- [0, M_PI]
    // floor(...)  --- [0, EXTRA_VERTEX_PER_PI]
    float dotProduct = vector1.dot(vector2);
    // make sure that dotProduct value is in acsof input range [-1, 1]
    dotProduct = MathUtils::clamp(dotProduct, -1.0f, 1.0f);
    // TODO: Use look up table for the dotProduct to extraVerticesNumber
    // computation, if needed.
    float angle = acosf(dotProduct);
    return (int)floor(angle / divisor);
}

void ShadowTessellator::checkOverflow(int used, int total, const char* bufferName) {
    LOG_ALWAYS_FATAL_IF(used > total, "Error: %s overflow!!! used %d, total %d", bufferName, used,
                        total);
}

};  // namespace uirenderer
};  // namespace android