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/*
* 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.
*/
#define LOG_TAG "OpenGLRenderer"
#include <math.h>
#include <utils/Log.h>
#include <utils/Vector.h>
#include "AmbientShadow.h"
#include "ShadowTessellator.h"
#include "Vertex.h"
namespace android {
namespace uirenderer {
/**
* Calculate the shadows as a triangle strips while alpha value as the
* shadow values.
*
* @param vertices The shadow caster's polygon, which is represented in a Vector3
* array.
* @param vertexCount The length of caster's polygon in terms of number of
* vertices.
* @param centroid3d The centroid of the shadow caster.
* @param heightFactor The factor showing the higher the object, the lighter the
* shadow.
* @param geomFactor The factor scaling the geometry expansion along the normal.
*
* @param shadowVertexBuffer Return an floating point array of (x, y, a)
* triangle strips mode.
*/
void AmbientShadow::createAmbientShadow(const Vector3* vertices, int vertexCount,
const Vector3& centroid3d, float heightFactor, float geomFactor,
VertexBuffer& shadowVertexBuffer) {
const int rays = SHADOW_RAY_COUNT;
const int layers = SHADOW_LAYER_COUNT;
// Validate the inputs.
if (vertexCount < 3 || heightFactor <= 0 || layers <= 0 || rays <= 0
|| geomFactor <= 0) {
#if DEBUG_SHADOW
ALOGE("Invalid input for createAmbientShadow(), early return!");
#endif
return;
}
Vector<Vector2> dir; // TODO: use C++11 unique_ptr
dir.setCapacity(rays);
float rayDist[rays];
float rayHeight[rays];
calculateRayDirections(rays, dir.editArray());
// Calculate the length and height of the points along the edge.
//
// The math here is:
// Intersect each ray (starting from the centroid) with the polygon.
for (int i = 0; i < rays; i++) {
int edgeIndex;
float edgeFraction;
float rayDistance;
calculateIntersection(vertices, vertexCount, centroid3d, dir[i], edgeIndex,
edgeFraction, rayDistance);
rayDist[i] = rayDistance;
if (edgeIndex < 0 || edgeIndex >= vertexCount) {
#if DEBUG_SHADOW
ALOGE("Invalid edgeIndex!");
#endif
edgeIndex = 0;
}
float h1 = vertices[edgeIndex].z;
float h2 = vertices[((edgeIndex + 1) % vertexCount)].z;
rayHeight[i] = h1 + edgeFraction * (h2 - h1);
}
// The output buffer length basically is roughly rays * layers, but since we
// need triangle strips, so we need to duplicate vertices to accomplish that.
AlphaVertex* shadowVertices = shadowVertexBuffer.alloc<AlphaVertex>(SHADOW_VERTEX_COUNT);
// Calculate the vertex of the shadows.
//
// The math here is:
// Along the edges of the polygon, for each intersection point P (generated above),
// calculate the normal N, which should be perpendicular to the edge of the
// polygon (represented by the neighbor intersection points) .
// Shadow's vertices will be generated as : P + N * scale.
int currentVertexIndex = 0;
for (int layerIndex = 0; layerIndex <= layers; layerIndex++) {
for (int rayIndex = 0; rayIndex < rays; rayIndex++) {
Vector2 normal(1.0f, 0.0f);
calculateNormal(rays, rayIndex, dir.array(), rayDist, normal);
float opacity = 1.0 / (1 + rayHeight[rayIndex] / heightFactor);
// The vertex should be start from rayDist[i] then scale the
// normalizeNormal!
Vector2 intersection = dir[rayIndex] * rayDist[rayIndex] +
Vector2(centroid3d.x, centroid3d.y);
float layerRatio = layerIndex / (float)(layers);
// The higher the intersection is, the further the ambient shadow expanded.
float expansionDist = rayHeight[rayIndex] / heightFactor *
geomFactor * (1 - layerRatio);
AlphaVertex::set(&shadowVertices[currentVertexIndex++],
intersection.x + normal.x * expansionDist,
intersection.y + normal.y * expansionDist,
layerRatio * opacity);
}
}
float centroidAlpha = 1.0 / (1 + centroid3d.z / heightFactor);
AlphaVertex::set(&shadowVertices[currentVertexIndex++],
centroid3d.x, centroid3d.y, centroidAlpha);
#if DEBUG_SHADOW
if (currentVertexIndex != SHADOW_VERTEX_COUNT) {
ALOGE("number of vertex generated for ambient shadow is wrong! "
"current: %d , expected: %d", currentVertexIndex, SHADOW_VERTEX_COUNT);
}
for (int i = 0; i < SHADOW_VERTEX_COUNT; i++) {
ALOGD("ambient shadow value: i %d, (x:%f, y:%f, a:%f)", i, shadowVertices[i].x,
shadowVertices[i].y, shadowVertices[i].alpha);
}
#endif
}
/**
* Generate an array of rays' direction vectors.
*
* @param rays The number of rays shooting out from the centroid.
* @param dir Return the array of ray vectors.
*/
void AmbientShadow::calculateRayDirections(int rays, Vector2* dir) {
float deltaAngle = 2 * M_PI / rays;
for (int i = 0; i < rays; i++) {
dir[i].x = sinf(deltaAngle * i);
dir[i].y = cosf(deltaAngle * i);
}
}
/**
* Calculate the intersection of a ray hitting the polygon.
*
* @param vertices The shadow caster's polygon, which is represented in a
* Vector3 array.
* @param vertexCount The length of caster's polygon in terms of number of vertices.
* @param start The starting point of the ray.
* @param dir The direction vector of the ray.
*
* @param outEdgeIndex Return the index of the segment (or index of the starting
* vertex) that ray intersect with.
* @param outEdgeFraction Return the fraction offset from the segment starting
* index.
* @param outRayDist Return the ray distance from centroid to the intersection.
*/
void AmbientShadow::calculateIntersection(const Vector3* vertices, int vertexCount,
const Vector3& start, const Vector2& dir, int& outEdgeIndex,
float& outEdgeFraction, float& outRayDist) {
float startX = start.x;
float startY = start.y;
float dirX = dir.x;
float dirY = dir.y;
// Start the search from the last edge from poly[len-1] to poly[0].
int p1 = vertexCount - 1;
for (int p2 = 0; p2 < vertexCount; p2++) {
float p1x = vertices[p1].x;
float p1y = vertices[p1].y;
float p2x = vertices[p2].x;
float p2y = vertices[p2].y;
// The math here is derived from:
// f(t, v) = p1x * (1 - t) + p2x * t - (startX + dirX * v) = 0;
// g(t, v) = p1y * (1 - t) + p2y * t - (startY + dirY * v) = 0;
float div = (dirX * (p1y - p2y) + dirY * p2x - dirY * p1x);
if (div != 0) {
float t = (dirX * (p1y - startY) + dirY * startX - dirY * p1x) / (div);
if (t > 0 && t <= 1) {
float t2 = (p1x * (startY - p2y)
+ p2x * (p1y - startY)
+ startX * (p2y - p1y)) / div;
if (t2 > 0) {
outEdgeIndex = p1;
outRayDist = t2;
outEdgeFraction = t;
return;
}
}
}
p1 = p2;
}
return;
};
/**
* Calculate the normal at the intersection point between a ray and the polygon.
*
* @param rays The total number of rays.
* @param currentRayIndex The index of the ray which the normal is based on.
* @param dir The array of the all the rays directions.
* @param rayDist The pre-computed ray distances array.
*
* @param normal Return the normal.
*/
void AmbientShadow::calculateNormal(int rays, int currentRayIndex,
const Vector2* dir, const float* rayDist, Vector2& normal) {
int preIndex = (currentRayIndex - 1 + rays) % rays;
int postIndex = (currentRayIndex + 1) % rays;
Vector2 p1 = dir[preIndex] * rayDist[preIndex];
Vector2 p2 = dir[postIndex] * rayDist[postIndex];
// Now the V (deltaX, deltaY) is the vector going CW around the poly.
Vector2 delta = p2 - p1;
if (delta.length() != 0) {
delta.normalize();
// Calculate the normal , which is CCW 90 rotate to the V.
// 90 degrees CCW about z-axis: (x, y, z) -> (-y, x, z)
normal.x = -delta.y;
normal.y = delta.x;
}
}
}; // namespace uirenderer
}; // namespace android