libs/hwui/FontRenderer.cpp

/*
 * Copyright (C) 2010 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 <SkGlyph.h>
#include <SkUtils.h>

#include <cutils/properties.h>

#include <utils/Log.h>

#include "Caches.h"
#include "Debug.h"
#include "FontRenderer.h"
#include "Rect.h"

namespace android {
namespace uirenderer {

///////////////////////////////////////////////////////////////////////////////
// FontRenderer
///////////////////////////////////////////////////////////////////////////////

static bool sLogFontRendererCreate = true;

FontRenderer::FontRenderer() {
    if (sLogFontRendererCreate) {
        INIT_LOGD("Creating FontRenderer");
    }

    mGammaTable = NULL;
    mInitialized = false;
    mMaxNumberOfQuads = 1024;
    mCurrentQuadIndex = 0;
    mLastQuadIndex = 0;

    mTextMesh = NULL;
    mCurrentCacheTexture = NULL;

    mLinearFiltering = false;

    mIndexBufferID = 0;

    mSmallCacheWidth = DEFAULT_TEXT_SMALL_CACHE_WIDTH;
    mSmallCacheHeight = DEFAULT_TEXT_SMALL_CACHE_HEIGHT;
    mLargeCacheWidth = DEFAULT_TEXT_LARGE_CACHE_WIDTH;
    mLargeCacheHeight = DEFAULT_TEXT_LARGE_CACHE_HEIGHT;

    char property[PROPERTY_VALUE_MAX];
    if (property_get(PROPERTY_TEXT_SMALL_CACHE_WIDTH, property, NULL) > 0) {
        mSmallCacheWidth = atoi(property);
    }

    if (property_get(PROPERTY_TEXT_SMALL_CACHE_HEIGHT, property, NULL) > 0) {
        mSmallCacheHeight = atoi(property);
    }

    if (property_get(PROPERTY_TEXT_LARGE_CACHE_WIDTH, property, NULL) > 0) {
        mLargeCacheWidth = atoi(property);
    }

    if (property_get(PROPERTY_TEXT_LARGE_CACHE_HEIGHT, property, NULL) > 0) {
        mLargeCacheHeight = atoi(property);
    }

    uint32_t maxTextureSize = (uint32_t) Caches::getInstance().maxTextureSize;
    mSmallCacheWidth = mSmallCacheWidth > maxTextureSize ? maxTextureSize : mSmallCacheWidth;
    mSmallCacheHeight = mSmallCacheHeight > maxTextureSize ? maxTextureSize : mSmallCacheHeight;
    mLargeCacheWidth = mLargeCacheWidth > maxTextureSize ? maxTextureSize : mLargeCacheWidth;
    mLargeCacheHeight = mLargeCacheHeight > maxTextureSize ? maxTextureSize : mLargeCacheHeight;

    if (sLogFontRendererCreate) {
        INIT_LOGD("  Text cache sizes, in pixels: %i x %i, %i x %i, %i x %i, %i x %i",
                mSmallCacheWidth, mSmallCacheHeight,
                mLargeCacheWidth, mLargeCacheHeight >> 1,
                mLargeCacheWidth, mLargeCacheHeight >> 1,
                mLargeCacheWidth, mLargeCacheHeight);
    }

    sLogFontRendererCreate = false;
}

FontRenderer::~FontRenderer() {
    for (uint32_t i = 0; i < mCacheTextures.size(); i++) {
        delete mCacheTextures[i];
    }
    mCacheTextures.clear();

    if (mInitialized) {
        // Unbinding the buffer shouldn't be necessary but it crashes with some drivers
        Caches::getInstance().unbindIndicesBuffer();
        glDeleteBuffers(1, &mIndexBufferID);

        delete[] mTextMesh;
    }

    Vector<Font*> fontsToDereference = mActiveFonts;
    for (uint32_t i = 0; i < fontsToDereference.size(); i++) {
        delete fontsToDereference[i];
    }
}

void FontRenderer::flushAllAndInvalidate() {
    if (mCurrentQuadIndex != 0) {
        issueDrawCommand();
    }

    for (uint32_t i = 0; i < mActiveFonts.size(); i++) {
        mActiveFonts[i]->invalidateTextureCache();
    }

    for (uint32_t i = 0; i < mCacheTextures.size(); i++) {
        mCacheTextures[i]->init();
    }

#if DEBUG_FONT_RENDERER
    uint16_t totalGlyphs = 0;
    for (uint32_t i = 0; i < mCacheTextures.size(); i++) {
        totalGlyphs += mCacheTextures[i]->getGlyphCount();
        // Erase caches, just as a debugging facility
        if (mCacheTextures[i]->getTexture()) {
            memset(mCacheTextures[i]->getTexture(), 0,
                    mCacheTextures[i]->getWidth() * mCacheTextures[i]->getHeight());
        }
    }
    ALOGD("Flushing caches: glyphs cached = %d", totalGlyphs);
#endif
}

void FontRenderer::flushLargeCaches() {
    // Start from 1; don't deallocate smallest/default texture
    for (uint32_t i = 1; i < mCacheTextures.size(); i++) {
        CacheTexture* cacheTexture = mCacheTextures[i];
        if (cacheTexture->getTexture()) {
            cacheTexture->init();
            for (uint32_t j = 0; j < mActiveFonts.size(); j++) {
                mActiveFonts[j]->invalidateTextureCache(cacheTexture);
            }
            cacheTexture->releaseTexture();
        }
    }
}

CacheTexture* FontRenderer::cacheBitmapInTexture(const SkGlyph& glyph,
        uint32_t* startX, uint32_t* startY) {
    for (uint32_t i = 0; i < mCacheTextures.size(); i++) {
        if (mCacheTextures[i]->fitBitmap(glyph, startX, startY)) {
            return mCacheTextures[i];
        }
    }
    // Could not fit glyph into current cache textures
    return NULL;
}

void FontRenderer::cacheBitmap(const SkGlyph& glyph, CachedGlyphInfo* cachedGlyph,
        uint32_t* retOriginX, uint32_t* retOriginY, bool precaching) {
    checkInit();
    cachedGlyph->mIsValid = false;
    // If the glyph is too tall, don't cache it
    if (glyph.fHeight + TEXTURE_BORDER_SIZE * 2 >
                mCacheTextures[mCacheTextures.size() - 1]->getHeight()) {
        ALOGE("Font size too large to fit in cache. width, height = %i, %i",
                (int) glyph.fWidth, (int) glyph.fHeight);
        return;
    }

    // Now copy the bitmap into the cache texture
    uint32_t startX = 0;
    uint32_t startY = 0;

    CacheTexture* cacheTexture = cacheBitmapInTexture(glyph, &startX, &startY);

    if (!cacheTexture) {
        if (!precaching) {
            // If the new glyph didn't fit and we are not just trying to precache it,
            // clear out the cache and try again
            flushAllAndInvalidate();
            cacheTexture = cacheBitmapInTexture(glyph, &startX, &startY);
        }

        if (!cacheTexture) {
            // either the glyph didn't fit or we're precaching and will cache it when we draw
            return;
        }
    }

    cachedGlyph->mCacheTexture = cacheTexture;

    *retOriginX = startX;
    *retOriginY = startY;

    uint32_t endX = startX + glyph.fWidth;
    uint32_t endY = startY + glyph.fHeight;

    uint32_t cacheWidth = cacheTexture->getWidth();

    if (!cacheTexture->getTexture()) {
        Caches::getInstance().activeTexture(0);
        // Large-glyph texture memory is allocated only as needed
        cacheTexture->allocateTexture();
    }

    uint8_t* cacheBuffer = cacheTexture->getTexture();
    uint8_t* bitmapBuffer = (uint8_t*) glyph.fImage;
    unsigned int stride = glyph.rowBytes();

    uint32_t cacheX = 0, bX = 0, cacheY = 0, bY = 0;

    for (cacheX = startX - TEXTURE_BORDER_SIZE; cacheX < endX + TEXTURE_BORDER_SIZE; cacheX++) {
        cacheBuffer[(startY - TEXTURE_BORDER_SIZE) * cacheWidth + cacheX] = 0;
        cacheBuffer[(endY + TEXTURE_BORDER_SIZE - 1) * cacheWidth + cacheX] = 0;
    }

    for (cacheY = startY - TEXTURE_BORDER_SIZE + 1;
            cacheY < endY + TEXTURE_BORDER_SIZE - 1; cacheY++) {
        cacheBuffer[cacheY * cacheWidth + startX - TEXTURE_BORDER_SIZE] = 0;
        cacheBuffer[cacheY * cacheWidth + endX + TEXTURE_BORDER_SIZE - 1] = 0;
    }

    if (mGammaTable) {
        for (cacheX = startX, bX = 0; cacheX < endX; cacheX++, bX++) {
            for (cacheY = startY, bY = 0; cacheY < endY; cacheY++, bY++) {
                uint8_t tempCol = bitmapBuffer[bY * stride + bX];
                cacheBuffer[cacheY * cacheWidth + cacheX] = mGammaTable[tempCol];
            }
        }
    } else {
        for (cacheX = startX, bX = 0; cacheX < endX; cacheX++, bX++) {
            for (cacheY = startY, bY = 0; cacheY < endY; cacheY++, bY++) {
                uint8_t tempCol = bitmapBuffer[bY * stride + bX];
                cacheBuffer[cacheY * cacheWidth + cacheX] = tempCol;
            }
        }
    }

    cachedGlyph->mIsValid = true;
}

CacheTexture* FontRenderer::createCacheTexture(int width, int height, bool allocate) {
    CacheTexture* cacheTexture = new CacheTexture(width, height);

    if (allocate) {
        Caches::getInstance().activeTexture(0);
        cacheTexture->allocateTexture();
    }

    return cacheTexture;
}

void FontRenderer::initTextTexture() {
    for (uint32_t i = 0; i < mCacheTextures.size(); i++) {
        delete mCacheTextures[i];
    }
    mCacheTextures.clear();

    mUploadTexture = false;
    mCacheTextures.push(createCacheTexture(mSmallCacheWidth, mSmallCacheHeight, true));
    mCacheTextures.push(createCacheTexture(mLargeCacheWidth, mLargeCacheHeight >> 1, false));
    mCacheTextures.push(createCacheTexture(mLargeCacheWidth, mLargeCacheHeight >> 1, false));
    mCacheTextures.push(createCacheTexture(mLargeCacheWidth, mLargeCacheHeight, false));
    mCurrentCacheTexture = mCacheTextures[0];
}

// Avoid having to reallocate memory and render quad by quad
void FontRenderer::initVertexArrayBuffers() {
    uint32_t numIndices = mMaxNumberOfQuads * 6;
    uint32_t indexBufferSizeBytes = numIndices * sizeof(uint16_t);
    uint16_t* indexBufferData = (uint16_t*) malloc(indexBufferSizeBytes);

    // Four verts, two triangles , six indices per quad
    for (uint32_t i = 0; i < mMaxNumberOfQuads; i++) {
        int i6 = i * 6;
        int i4 = i * 4;

        indexBufferData[i6 + 0] = i4 + 0;
        indexBufferData[i6 + 1] = i4 + 1;
        indexBufferData[i6 + 2] = i4 + 2;

        indexBufferData[i6 + 3] = i4 + 0;
        indexBufferData[i6 + 4] = i4 + 2;
        indexBufferData[i6 + 5] = i4 + 3;
    }

    glGenBuffers(1, &mIndexBufferID);
    Caches::getInstance().bindIndicesBuffer(mIndexBufferID);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, indexBufferSizeBytes, indexBufferData, GL_STATIC_DRAW);

    free(indexBufferData);

    uint32_t coordSize = 2;
    uint32_t uvSize = 2;
    uint32_t vertsPerQuad = 4;
    uint32_t vertexBufferSize = mMaxNumberOfQuads * vertsPerQuad * coordSize * uvSize;
    mTextMesh = new float[vertexBufferSize];
}

// We don't want to allocate anything unless we actually draw text
void FontRenderer::checkInit() {
    if (mInitialized) {
        return;
    }

    initTextTexture();
    initVertexArrayBuffers();

    mInitialized = true;
}

void FontRenderer::updateDrawParams() {
    if (mCurrentQuadIndex != mLastQuadIndex) {
        mDrawOffsets.add((uint16_t*)(mLastQuadIndex * sizeof(uint16_t) * 6));
        mDrawCounts.add(mCurrentQuadIndex - mLastQuadIndex);
        mDrawCacheTextures.add(mCurrentCacheTexture);
        mLastQuadIndex = mCurrentQuadIndex;
    }
}

void FontRenderer::checkTextureUpdate() {
    if (!mUploadTexture) {
        return;
    }

    Caches& caches = Caches::getInstance();
    GLuint lastTextureId = 0;
    // Iterate over all the cache textures and see which ones need to be updated
    for (uint32_t i = 0; i < mCacheTextures.size(); i++) {
        CacheTexture* cacheTexture = mCacheTextures[i];
        if (cacheTexture->isDirty() && cacheTexture->getTexture()) {
            // Can't copy inner rect; glTexSubimage expects pointer to deal with entire buffer
            // of data. So expand the dirty rect to the encompassing horizontal stripe.
            const Rect* dirtyRect = cacheTexture->getDirtyRect();
            uint32_t x = 0;
            uint32_t y = dirtyRect->top;
            uint32_t width = cacheTexture->getWidth();
            uint32_t height = dirtyRect->getHeight();
            void* textureData = cacheTexture->getTexture() + y * width;

            if (cacheTexture->getTextureId() != lastTextureId) {
                lastTextureId = cacheTexture->getTextureId();
                caches.activeTexture(0);
                glBindTexture(GL_TEXTURE_2D, lastTextureId);
            }
#if DEBUG_FONT_RENDERER
            ALOGD("glTexSubimage for cacheTexture %d: x, y, width height = %d, %d, %d, %d",
                    i, x, y, width, height);
#endif
            glTexSubImage2D(GL_TEXTURE_2D, 0, x, y, width, height,
                    GL_ALPHA, GL_UNSIGNED_BYTE, textureData);
            cacheTexture->setDirty(false);
        }
    }

    mUploadTexture = false;
}

void FontRenderer::issueDrawCommand() {
    updateDrawParams();
    checkTextureUpdate();

    Caches& caches = Caches::getInstance();
    caches.bindIndicesBuffer(mIndexBufferID);
    if (!mDrawn) {
        float* buffer = mTextMesh;
        int offset = 2;

        bool force = caches.unbindMeshBuffer();
        caches.bindPositionVertexPointer(force, buffer);
        caches.bindTexCoordsVertexPointer(force, buffer + offset);
    }

    for (uint32_t i = 0; i < mDrawOffsets.size(); i++) {
        uint16_t* offset = mDrawOffsets[i];
        uint32_t count = mDrawCounts[i];
        CacheTexture* texture = mDrawCacheTextures[i];

        caches.activeTexture(0);
        glBindTexture(GL_TEXTURE_2D, texture->getTextureId());

        texture->setLinearFiltering(mLinearFiltering, false);

        glDrawElements(GL_TRIANGLES, count * 6, GL_UNSIGNED_SHORT, offset);
    }

    mDrawn = true;

    mCurrentQuadIndex = 0;
    mLastQuadIndex = 0;
    mDrawOffsets.clear();
    mDrawCounts.clear();
    mDrawCacheTextures.clear();
}

void FontRenderer::appendMeshQuadNoClip(float x1, float y1, float u1, float v1,
        float x2, float y2, float u2, float v2, float x3, float y3, float u3, float v3,
        float x4, float y4, float u4, float v4, CacheTexture* texture) {
    if (texture != mCurrentCacheTexture) {
        updateDrawParams();
        // Now use the new texture id
        mCurrentCacheTexture = texture;
    }

    const uint32_t vertsPerQuad = 4;
    const uint32_t floatsPerVert = 4;
    float* currentPos = mTextMesh + mCurrentQuadIndex * vertsPerQuad * floatsPerVert;

    (*currentPos++) = x1;
    (*currentPos++) = y1;
    (*currentPos++) = u1;
    (*currentPos++) = v1;

    (*currentPos++) = x2;
    (*currentPos++) = y2;
    (*currentPos++) = u2;
    (*currentPos++) = v2;

    (*currentPos++) = x3;
    (*currentPos++) = y3;
    (*currentPos++) = u3;
    (*currentPos++) = v3;

    (*currentPos++) = x4;
    (*currentPos++) = y4;
    (*currentPos++) = u4;
    (*currentPos++) = v4;

    mCurrentQuadIndex++;
}

void FontRenderer::appendMeshQuad(float x1, float y1, float u1, float v1,
        float x2, float y2, float u2, float v2, float x3, float y3, float u3, float v3,
        float x4, float y4, float u4, float v4, CacheTexture* texture) {

    if (mClip &&
            (x1 > mClip->right || y1 < mClip->top || x2 < mClip->left || y4 > mClip->bottom)) {
        return;
    }

    appendMeshQuadNoClip(x1, y1, u1, v1, x2, y2, u2, v2, x3, y3, u3, v3, x4, y4, u4, v4, texture);

    if (mBounds) {
        mBounds->left = fmin(mBounds->left, x1);
        mBounds->top = fmin(mBounds->top, y3);
        mBounds->right = fmax(mBounds->right, x3);
        mBounds->bottom = fmax(mBounds->bottom, y1);
    }

    if (mCurrentQuadIndex == mMaxNumberOfQuads) {
        issueDrawCommand();
    }
}

void FontRenderer::appendRotatedMeshQuad(float x1, float y1, float u1, float v1,
        float x2, float y2, float u2, float v2, float x3, float y3, float u3, float v3,
        float x4, float y4, float u4, float v4, CacheTexture* texture) {

    appendMeshQuadNoClip(x1, y1, u1, v1, x2, y2, u2, v2, x3, y3, u3, v3, x4, y4, u4, v4, texture);

    if (mBounds) {
        mBounds->left = fmin(mBounds->left, fmin(x1, fmin(x2, fmin(x3, x4))));
        mBounds->top = fmin(mBounds->top, fmin(y1, fmin(y2, fmin(y3, y4))));
        mBounds->right = fmax(mBounds->right, fmax(x1, fmax(x2, fmax(x3, x4))));
        mBounds->bottom = fmax(mBounds->bottom, fmax(y1, fmax(y2, fmax(y3, y4))));
    }

    if (mCurrentQuadIndex == mMaxNumberOfQuads) {
        issueDrawCommand();
    }
}

void FontRenderer::setFont(SkPaint* paint, uint32_t fontId, float fontSize) {
    int flags = 0;
    if (paint->isFakeBoldText()) {
        flags |= Font::kFakeBold;
    }

    const float skewX = paint->getTextSkewX();
    uint32_t italicStyle = *(uint32_t*) &skewX;
    const float scaleXFloat = paint->getTextScaleX();
    uint32_t scaleX = *(uint32_t*) &scaleXFloat;
    SkPaint::Style style = paint->getStyle();
    const float strokeWidthFloat = paint->getStrokeWidth();
    uint32_t strokeWidth = *(uint32_t*) &strokeWidthFloat;
    mCurrentFont = Font::create(this, fontId, fontSize, flags, italicStyle,
            scaleX, style, strokeWidth);

}

FontRenderer::DropShadow FontRenderer::renderDropShadow(SkPaint* paint, const char *text,
        uint32_t startIndex, uint32_t len, int numGlyphs, uint32_t radius, const float* positions) {
    checkInit();

    if (!mCurrentFont) {
        DropShadow image;
        image.width = 0;
        image.height = 0;
        image.image = NULL;
        image.penX = 0;
        image.penY = 0;
        return image;
    }

    mDrawn = false;
    mClip = NULL;
    mBounds = NULL;

    Rect bounds;
    mCurrentFont->measure(paint, text, startIndex, len, numGlyphs, &bounds, positions);

    uint32_t paddedWidth = (uint32_t) (bounds.right - bounds.left) + 2 * radius;
    uint32_t paddedHeight = (uint32_t) (bounds.top - bounds.bottom) + 2 * radius;
    uint8_t* dataBuffer = new uint8_t[paddedWidth * paddedHeight];

    for (uint32_t i = 0; i < paddedWidth * paddedHeight; i++) {
        dataBuffer[i] = 0;
    }

    int penX = radius - bounds.left;
    int penY = radius - bounds.bottom;

    mCurrentFont->render(paint, text, startIndex, len, numGlyphs, penX, penY,
            Font::BITMAP, dataBuffer, paddedWidth, paddedHeight, NULL, positions);
    blurImage(dataBuffer, paddedWidth, paddedHeight, radius);

    DropShadow image;
    image.width = paddedWidth;
    image.height = paddedHeight;
    image.image = dataBuffer;
    image.penX = penX;
    image.penY = penY;

    return image;
}

void FontRenderer::initRender(const Rect* clip, Rect* bounds) {
    checkInit();

    mDrawn = false;
    mBounds = bounds;
    mClip = clip;
}

void FontRenderer::finishRender() {
    mBounds = NULL;
    mClip = NULL;

    if (mCurrentQuadIndex != 0) {
        issueDrawCommand();
    }
}

void FontRenderer::precache(SkPaint* paint, const char* text, int numGlyphs) {
    int flags = 0;
    if (paint->isFakeBoldText()) {
        flags |= Font::kFakeBold;
    }
    const float skewX = paint->getTextSkewX();
    uint32_t italicStyle = *(uint32_t*) &skewX;
    const float scaleXFloat = paint->getTextScaleX();
    uint32_t scaleX = *(uint32_t*) &scaleXFloat;
    SkPaint::Style style = paint->getStyle();
    const float strokeWidthFloat = paint->getStrokeWidth();
    uint32_t strokeWidth = *(uint32_t*) &strokeWidthFloat;
    float fontSize = paint->getTextSize();
    Font* font = Font::create(this, SkTypeface::UniqueID(paint->getTypeface()),
            fontSize, flags, italicStyle, scaleX, style, strokeWidth);

    font->precache(paint, text, numGlyphs);
}

bool FontRenderer::renderText(SkPaint* paint, const Rect* clip, const char *text,
        uint32_t startIndex, uint32_t len, int numGlyphs, int x, int y, Rect* bounds) {
    if (!mCurrentFont) {
        ALOGE("No font set");
        return false;
    }

    initRender(clip, bounds);
    mCurrentFont->render(paint, text, startIndex, len, numGlyphs, x, y);
    finishRender();

    return mDrawn;
}

bool FontRenderer::renderPosText(SkPaint* paint, const Rect* clip, const char *text,
        uint32_t startIndex, uint32_t len, int numGlyphs, int x, int y,
        const float* positions, Rect* bounds) {
    if (!mCurrentFont) {
        ALOGE("No font set");
        return false;
    }

    initRender(clip, bounds);
    mCurrentFont->render(paint, text, startIndex, len, numGlyphs, x, y, positions);
    finishRender();

    return mDrawn;
}

bool FontRenderer::renderTextOnPath(SkPaint* paint, const Rect* clip, const char *text,
        uint32_t startIndex, uint32_t len, int numGlyphs, SkPath* path,
        float hOffset, float vOffset, Rect* bounds) {
    if (!mCurrentFont) {
        ALOGE("No font set");
        return false;
    }

    initRender(clip, bounds);
    mCurrentFont->render(paint, text, startIndex, len, numGlyphs, path, hOffset, vOffset);
    finishRender();

    return mDrawn;
}

void FontRenderer::removeFont(const Font* font) {
    for (uint32_t ct = 0; ct < mActiveFonts.size(); ct++) {
        if (mActiveFonts[ct] == font) {
            mActiveFonts.removeAt(ct);
            break;
        }
    }

    if (mCurrentFont == font) {
        mCurrentFont = NULL;
    }
}

void FontRenderer::computeGaussianWeights(float* weights, int32_t radius) {
    // Compute gaussian weights for the blur
    // e is the euler's number
    float e = 2.718281828459045f;
    float pi = 3.1415926535897932f;
    // g(x) = ( 1 / sqrt( 2 * pi ) * sigma) * e ^ ( -x^2 / 2 * sigma^2 )
    // x is of the form [-radius .. 0 .. radius]
    // and sigma varies with radius.
    // Based on some experimental radius values and sigma's
    // we approximately fit sigma = f(radius) as
    // sigma = radius * 0.3  + 0.6
    // The larger the radius gets, the more our gaussian blur
    // will resemble a box blur since with large sigma
    // the gaussian curve begins to lose its shape
    float sigma = 0.3f * (float) radius + 0.6f;

    // Now compute the coefficints
    // We will store some redundant values to save some math during
    // the blur calculations
    // precompute some values
    float coeff1 = 1.0f / (sqrt( 2.0f * pi ) * sigma);
    float coeff2 = - 1.0f / (2.0f * sigma * sigma);

    float normalizeFactor = 0.0f;
    for (int32_t r = -radius; r <= radius; r ++) {
        float floatR = (float) r;
        weights[r + radius] = coeff1 * pow(e, floatR * floatR * coeff2);
        normalizeFactor += weights[r + radius];
    }

    //Now we need to normalize the weights because all our coefficients need to add up to one
    normalizeFactor = 1.0f / normalizeFactor;
    for (int32_t r = -radius; r <= radius; r ++) {
        weights[r + radius] *= normalizeFactor;
    }
}

void FontRenderer::horizontalBlur(float* weights, int32_t radius,
        const uint8_t* source, uint8_t* dest, int32_t width, int32_t height) {
    float blurredPixel = 0.0f;
    float currentPixel = 0.0f;

    for (int32_t y = 0; y < height; y ++) {

        const uint8_t* input = source + y * width;
        uint8_t* output = dest + y * width;

        for (int32_t x = 0; x < width; x ++) {
            blurredPixel = 0.0f;
            const float* gPtr = weights;
            // Optimization for non-border pixels
            if (x > radius && x < (width - radius)) {
                const uint8_t *i = input + (x - radius);
                for (int r = -radius; r <= radius; r ++) {
                    currentPixel = (float) (*i);
                    blurredPixel += currentPixel * gPtr[0];
                    gPtr++;
                    i++;
                }
            } else {
                for (int32_t r = -radius; r <= radius; r ++) {
                    // Stepping left and right away from the pixel
                    int validW = x + r;
                    if (validW < 0) {
                        validW = 0;
                    }
                    if (validW > width - 1) {
                        validW = width - 1;
                    }

                    currentPixel = (float) input[validW];
                    blurredPixel += currentPixel * gPtr[0];
                    gPtr++;
                }
            }
            *output = (uint8_t)blurredPixel;
            output ++;
        }
    }
}

void FontRenderer::verticalBlur(float* weights, int32_t radius,
        const uint8_t* source, uint8_t* dest, int32_t width, int32_t height) {
    float blurredPixel = 0.0f;
    float currentPixel = 0.0f;

    for (int32_t y = 0; y < height; y ++) {
        uint8_t* output = dest + y * width;

        for (int32_t x = 0; x < width; x ++) {
            blurredPixel = 0.0f;
            const float* gPtr = weights;
            const uint8_t* input = source + x;
            // Optimization for non-border pixels
            if (y > radius && y < (height - radius)) {
                const uint8_t *i = input + ((y - radius) * width);
                for (int32_t r = -radius; r <= radius; r ++) {
                    currentPixel = (float)(*i);
                    blurredPixel += currentPixel * gPtr[0];
                    gPtr++;
                    i += width;
                }
            } else {
                for (int32_t r = -radius; r <= radius; r ++) {
                    int validH = y + r;
                    // Clamp to zero and width
                    if (validH < 0) {
                        validH = 0;
                    }
                    if (validH > height - 1) {
                        validH = height - 1;
                    }

                    const uint8_t *i = input + validH * width;
                    currentPixel = (float) (*i);
                    blurredPixel += currentPixel * gPtr[0];
                    gPtr++;
                }
            }
            *output = (uint8_t) blurredPixel;
            output++;
        }
    }
}


void FontRenderer::blurImage(uint8_t *image, int32_t width, int32_t height, int32_t radius) {
    float *gaussian = new float[2 * radius + 1];
    computeGaussianWeights(gaussian, radius);

    uint8_t* scratch = new uint8_t[width * height];

    horizontalBlur(gaussian, radius, image, scratch, width, height);
    verticalBlur(gaussian, radius, scratch, image, width, height);

    delete[] gaussian;
    delete[] scratch;
}

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