sw_engine Raster: Improving image quality in image scale down

An average value sampled based on adjacent pixels of the target pixel is used.

diff --git a/src/lib/sw_engine/tvgSwRaster.cpp b/src/lib/sw_engine/tvgSwRaster.cpp
index 3cc262f..cc8b15e 100644 (file)
--- a/src/lib/sw_engine/tvgSwRaster.cpp
+++ b/src/lib/sw_engine/tvgSwRaster.cpp
@@ -113,6 +113,26 @@ static uint32_t _applyBilinearInterpolation(const uint32_t *img, uint32_t w, uin
     return COLOR_INTERPOLATE(COLOR_INTERPOLATE(c1, 255 - dX, c2, dX), 255 - dY, COLOR_INTERPOLATE(c4, 255 - dX, c3, dX), dY);
 }
 
+static uint32_t _average2Nx2NPixel(SwSurface* surface, const uint32_t *img, uint32_t w, uint32_t h, uint32_t rX, uint32_t rY, uint32_t n)
+{
+    uint32_t c[4] = { 0 };
+    auto n2 = n * n;
+    auto source = img + rX - n + (rY - n) * w;
+    for (auto y = rY - n; y < rY + n; ++y) {
+        auto src = source;
+        for (auto x = rX - n; x < rX + n; ++x, ++src) {
+            c[0] += *src >> 24;
+            c[1] += (*src >> 16) & 0xff;
+            c[2] += (*src >> 8) & 0xff;
+            c[3] += *src & 0xff;
+        }
+        source += w;
+    }
+    for (auto i = 0; i < 4; ++i) {
+        c[i] = (c[i] >> 2) / n2;
+    }
+    return (c[0] << 24) | (c[1] << 16) | (c[2] << 8) | c[3];
+}
 
 /************************************************************************/
 /* Rect                                                                 */
@@ -332,6 +352,7 @@ static bool _rasterTranslucentImageRle(SwSurface* surface, const SwRleData* rle,
     return true;
 }
 
+
 static bool _rasterTranslucentUpScaleImageRle(SwSurface* surface, const SwRleData* rle, uint32_t *img, uint32_t w, uint32_t h, uint32_t opacity, const Matrix* invTransform)
 {
     auto span = rle->spans;
@@ -356,6 +377,30 @@ static bool _rasterTranslucentUpScaleImageRle(SwSurface* surface, const SwRleDat
 }
 
 
+static bool _rasterTranslucentDownScaleImageRle(SwSurface* surface, const SwRleData* rle, uint32_t *img, uint32_t w, uint32_t h, uint32_t opacity, const Matrix* invTransform, float scaling)
+{
+    uint32_t halfScaling = static_cast<uint32_t>(0.5f / scaling);
+    if (halfScaling == 0) halfScaling = 1;
+    auto span = rle->spans;
+    for (uint32_t i = 0; i < rle->size; ++i, ++span) {
+        auto ey1 = span->y * invTransform->e12 + invTransform->e13;
+        auto ey2 = span->y * invTransform->e22 + invTransform->e23;
+        auto dst = &surface->buffer[span->y * surface->stride + span->x];
+        auto alpha = ALPHA_MULTIPLY(span->coverage, opacity);
+        for (uint32_t x = 0; x < span->len; ++x, ++dst) {
+            auto rX = static_cast<uint32_t>(roundf((span->x + x) * invTransform->e11 + ey1));
+            auto rY = static_cast<uint32_t>(roundf((span->x + x) * invTransform->e21 + ey2));
+            if (rX >= w || rY >= h) continue;
+            uint32_t src;
+            if (rX < halfScaling || rY < halfScaling || rX >= w - halfScaling || rY >= h - halfScaling) src = ALPHA_BLEND(img[rY * w + rX], alpha);     //TODO: need to use image's stride
+            else src = ALPHA_BLEND(_average2Nx2NPixel(surface, img, w, h, rX, rY, halfScaling), alpha);     //TODO: need to use image's stride
+            *dst = src + ALPHA_BLEND(*dst, 255 - surface->blender.alpha(src));
+        }
+    }
+    return true;
+}
+
+
 static bool _rasterImageRle(SwSurface* surface, SwRleData* rle, uint32_t *img, uint32_t w, uint32_t h)
 {
     auto span = rle->spans;
@@ -416,6 +461,30 @@ static bool _rasterUpScaleImageRle(SwSurface* surface, SwRleData* rle, uint32_t
 }
 
 
+static bool _rasterDownScaleImageRle(SwSurface* surface, SwRleData* rle, uint32_t *img, uint32_t w, uint32_t h, const Matrix* invTransform, float scaling)
+{
+    uint32_t halfScaling = static_cast<uint32_t>(0.5f / scaling);
+    if (halfScaling == 0) halfScaling = 1;
+    auto span = rle->spans;
+
+    for (uint32_t i = 0; i < rle->size; ++i, ++span) {
+        auto ey1 = span->y * invTransform->e12 + invTransform->e13;
+        auto ey2 = span->y * invTransform->e22 + invTransform->e23;
+        auto dst = &surface->buffer[span->y * surface->stride + span->x];
+        for (uint32_t x = 0; x < span->len; ++x, ++dst) {
+            auto rX = static_cast<uint32_t>(roundf((span->x + x) * invTransform->e11 + ey1));
+            auto rY = static_cast<uint32_t>(roundf((span->x + x) * invTransform->e21 + ey2));
+            if (rX >= w || rY >= h) continue;
+            uint32_t src;
+            if (rX < halfScaling || rY < halfScaling || rX >= w - halfScaling || rY >= h - halfScaling) src = ALPHA_BLEND(img[rY * w + rX], span->coverage);    //TODO: need to use image's stride
+            else src = ALPHA_BLEND(_average2Nx2NPixel(surface, img, w, h, rX, rY, halfScaling), span->coverage);    //TODO: need to use image's stride
+            *dst = src + ALPHA_BLEND(*dst, 255 - surface->blender.alpha(src));
+        }
+    }
+    return true;
+}
+
+
 static bool _translucentImage(SwSurface* surface, const uint32_t *img, uint32_t w, TVG_UNUSED uint32_t h, uint32_t opacity, const SwBBox& region, const Matrix* invTransform)
 {
     auto dbuffer = &surface->buffer[region.min.y * surface->stride + region.min.x];
@@ -601,6 +670,105 @@ static bool _rasterTranslucentUpScaleImage(SwSurface* surface, const uint32_t *i
 }
 
 
+static bool _translucentDownScaleImage(SwSurface* surface, const uint32_t *img, uint32_t w, TVG_UNUSED uint32_t h, uint32_t opacity, const SwBBox& region, const Matrix* invTransform, float scaling)
+{
+    uint32_t halfScaling = static_cast<uint32_t>(0.5f / scaling);
+    if (halfScaling == 0) halfScaling = 1;
+    auto dbuffer = &surface->buffer[region.min.y * surface->stride + region.min.x];
+
+    for (auto y = region.min.y; y < region.max.y; ++y) {
+        auto dst = dbuffer;
+        auto ey1 = y * invTransform->e12 + invTransform->e13;
+        auto ey2 = y * invTransform->e22 + invTransform->e23;
+        for (auto x = region.min.x; x < region.max.x; ++x, ++dst) {
+            auto rX = static_cast<uint32_t>(roundf(x * invTransform->e11 + ey1));
+            auto rY = static_cast<uint32_t>(roundf(x * invTransform->e21 + ey2));
+            if (rX >= w || rY >= h) continue;
+            uint32_t src;
+            if (rX < halfScaling || rY < halfScaling || rX >= w - halfScaling || rY >= h - halfScaling) src = ALPHA_BLEND(img[rX + (rY * w)], opacity);
+            else src = ALPHA_BLEND(_average2Nx2NPixel(surface, img, w, h, rX, rY, halfScaling), opacity);
+            *dst = src + ALPHA_BLEND(*dst, 255 - surface->blender.alpha(src));
+        }
+        dbuffer += surface->stride;
+    }
+    return true;
+}
+
+
+static bool _translucentDownScaleImageAlphaMask(SwSurface* surface, const uint32_t *img, uint32_t w, TVG_UNUSED uint32_t h, uint32_t opacity, const SwBBox& region, const Matrix* invTransform, float scaling)
+{
+    TVGLOG("SW_ENGINE", "Transformed Image Alpha Mask Composition");
+    uint32_t halfScaling = static_cast<uint32_t>(0.5f / scaling);
+    if (halfScaling == 0) halfScaling = 1;
+
+    auto dbuffer = &surface->buffer[region.min.y * surface->stride + region.min.x];
+    auto cbuffer = &surface->compositor->image.data[region.min.y * surface->stride + region.min.x];
+
+    for (auto y = region.min.y; y < region.max.y; ++y) {
+        auto dst = dbuffer;
+        auto cmp = cbuffer;
+        float ey1 = y * invTransform->e12 + invTransform->e13;
+        float ey2 = y * invTransform->e22 + invTransform->e23;
+        for (auto x = region.min.x; x < region.max.x; ++x, ++dst, ++cmp) {
+            auto rX = static_cast<uint32_t>(roundf(x * invTransform->e11 + ey1));
+            auto rY = static_cast<uint32_t>(roundf(x * invTransform->e21 + ey2));
+            if (rX >= w || rY >= h) continue;
+            uint32_t src;
+            if (rX < halfScaling || rY < halfScaling || rX >= w - halfScaling || rY >= h - halfScaling) src = ALPHA_BLEND(img[rX + (rY * w)], ALPHA_MULTIPLY(opacity, surface->blender.alpha(*cmp)));  //TODO: need to use image's stride
+            else src = ALPHA_BLEND(_average2Nx2NPixel(surface, img, w, h, rX, rY, halfScaling), ALPHA_MULTIPLY(opacity, surface->blender.alpha(*cmp)));  //TODO: need to use image's stride
+            *dst = src + ALPHA_BLEND(*dst, 255 - surface->blender.alpha(src));
+        }
+        dbuffer += surface->stride;
+        cbuffer += surface->stride;
+    }
+    return true;
+}
+
+
+static bool _translucentDownScaleImageInvAlphaMask(SwSurface* surface, const uint32_t *img, uint32_t w, uint32_t h, uint32_t opacity, const SwBBox& region, const Matrix* invTransform, float scaling)
+{
+    TVGLOG("SW_ENGINE", "Transformed Image Inverse Alpha Mask Composition");
+    uint32_t halfScaling = static_cast<uint32_t>(0.5f / scaling);
+    if (halfScaling == 0) halfScaling = 1;
+
+    auto dbuffer = &surface->buffer[region.min.y * surface->stride + region.min.x];
+    auto cbuffer = &surface->compositor->image.data[region.min.y * surface->stride + region.min.x];
+
+    for (auto y = region.min.y; y < region.max.y; ++y) {
+        auto dst = dbuffer;
+        auto cmp = cbuffer;
+        float ey1 = y * invTransform->e12 + invTransform->e13;
+        float ey2 = y * invTransform->e22 + invTransform->e23;
+        for (auto x = region.min.x; x < region.max.x; ++x, ++dst, ++cmp) {
+            auto rX = static_cast<uint32_t>(roundf(x * invTransform->e11 + ey1));
+            auto rY = static_cast<uint32_t>(roundf(x * invTransform->e21 + ey2));
+            if (rX >= w || rY >= h) continue;
+            uint32_t src;
+            if (rX < halfScaling || rY < halfScaling || rX >= w - halfScaling || rY >= h - halfScaling) src = ALPHA_BLEND(img[rX + (rY * w)], ALPHA_MULTIPLY(opacity, 255 - surface->blender.alpha(*cmp)));  //TODO: need to use image's stride
+            else src = ALPHA_BLEND(_average2Nx2NPixel(surface, img, w, h, rX, rY, halfScaling), ALPHA_MULTIPLY(opacity, 255 - surface->blender.alpha(*cmp)));  //TODO: need to use image's stride
+            *dst = src + ALPHA_BLEND(*dst, 255 - surface->blender.alpha(src));
+        }
+        dbuffer += surface->stride;
+        cbuffer += surface->stride;
+    }
+    return true;
+}
+
+
+static bool _rasterTranslucentDownScaleImage(SwSurface* surface, const uint32_t *img, uint32_t w, uint32_t h, uint32_t opacity, const SwBBox& region, const Matrix* invTransform, float scaling)
+{
+    if (surface->compositor) {
+        if (surface->compositor->method == CompositeMethod::AlphaMask) {
+            return _translucentDownScaleImageAlphaMask(surface, img, w, h, opacity, region, invTransform, scaling);
+        }
+        if (surface->compositor->method == CompositeMethod::InvAlphaMask) {
+            return _translucentDownScaleImageInvAlphaMask(surface, img, w, h, opacity, region, invTransform, scaling);
+        }
+    }
+    return _translucentDownScaleImage(surface, img, w, h, opacity, region, invTransform, scaling);
+}
+
+
 static bool _translucentImage(SwSurface* surface, uint32_t *img, uint32_t w, uint32_t h, uint32_t opacity, const SwBBox& region)
 {
     auto dbuffer = &surface->buffer[region.min.y * surface->stride + region.min.x];
@@ -744,6 +912,31 @@ static bool _rasterUpScaleImage(SwSurface* surface, const uint32_t *img, uint32_
     }
     return true;
 }
+
+
+static bool _rasterDownScaleImage(SwSurface* surface, const uint32_t *img, uint32_t w, uint32_t h, const SwBBox& region, const Matrix* invTransform, float scaling)
+{
+    uint32_t halfScaling = static_cast<uint32_t>(0.5f / scaling);
+
+    if (halfScaling == 0) halfScaling = 1;
+    for (auto y = region.min.y; y < region.max.y; ++y) {
+        auto dst = &surface->buffer[y * surface->stride + region.min.x];
+        auto ey1 = y * invTransform->e12 + invTransform->e13;
+        auto ey2 = y * invTransform->e22 + invTransform->e23;
+        for (auto x = region.min.x; x < region.max.x; ++x, ++dst) {
+            auto rX = static_cast<uint32_t>(roundf(x * invTransform->e11 + ey1));
+            auto rY = static_cast<uint32_t>(roundf(x * invTransform->e21 + ey2));
+            if (rX >= w || rY >= h) continue;
+            uint32_t src;
+            if (rX < halfScaling || rY < halfScaling || rX >= w - halfScaling || rY >= h - halfScaling) src = img[rX + (rY * w)];
+            else src = _average2Nx2NPixel(surface, img, w, h, rX, rY, halfScaling);
+            *dst = src + ALPHA_BLEND(*dst, 255 - surface->blender.alpha(src));
+        }
+    }
+    return true;
+}
+
+
 /************************************************************************/
 /* Gradient                                                             */
 /************************************************************************/
@@ -1364,15 +1557,19 @@ bool rasterClear(SwSurface* surface)
 bool rasterImage(SwSurface* surface, SwImage* image, const Matrix* transform, const SwBBox& bbox, uint32_t opacity)
 {
     Matrix invTransform;
-    auto isUpScaling = false;
+    float scaling = 1.0f;
 
     if (transform) {
         if (!_inverse(transform, &invTransform)) return false;
-        isUpScaling = (transform->e11 * transform->e11) + (transform->e21 * transform->e21) > 1 ? true : false;
+        scaling = sqrt((transform->e11 * transform->e11) + (transform->e21 * transform->e21));
+        auto scalingY = sqrt((transform->e22 * transform->e22) + (transform->e12 * transform->e12));
+        //TODO:If the x and y axis scaling is different, a separate algorithm for each axis should be applied.
+        if (scaling != scalingY) scaling = 1.0f;
     }
     else invTransform = {1, 0, 0, 0, 1, 0, 0, 0, 1};
 
     auto translucent = _translucent(surface, opacity);
+    const float downScalingFactor = 0.5f;
 
     if (image->rle) {
         //Fast track
@@ -1382,11 +1579,13 @@ bool rasterImage(SwSurface* surface, SwImage* image, const Matrix* transform, co
             return _rasterImageRle(surface, image->rle, image->data, image->w, image->h);
         } else {
             if (translucent) {
-                if (isUpScaling) return _rasterTranslucentUpScaleImageRle(surface, image->rle, image->data, image->w, image->h, opacity, &invTransform);
-                return _rasterTranslucentImageRle(surface, image->rle, image->data, image->w, image->h, opacity, &invTransform);
+                if (fabsf(scaling - 1.0f) <= FLT_EPSILON) return _rasterTranslucentImageRle(surface, image->rle, image->data, image->w, image->h, opacity, &invTransform);
+                else if (scaling < downScalingFactor) return _rasterTranslucentDownScaleImageRle(surface, image->rle, image->data, image->w, image->h, opacity, &invTransform, scaling);
+                else return _rasterTranslucentUpScaleImageRle(surface, image->rle, image->data, image->w, image->h, opacity, &invTransform);
             }
-            if (isUpScaling) return _rasterUpScaleImageRle(surface, image->rle, image->data, image->w, image->h, &invTransform);
-            return _rasterImageRle(surface, image->rle, image->data, image->w, image->h, &invTransform);
+            if (fabsf(scaling - 1.0f) <= FLT_EPSILON) return _rasterImageRle(surface, image->rle, image->data, image->w, image->h, &invTransform);
+            else if (scaling < downScalingFactor) return _rasterDownScaleImageRle(surface, image->rle, image->data, image->w, image->h, &invTransform, scaling);
+            else return _rasterUpScaleImageRle(surface, image->rle, image->data, image->w, image->h, &invTransform);
         }
     }
     else {
@@ -1397,11 +1596,13 @@ bool rasterImage(SwSurface* surface, SwImage* image, const Matrix* transform, co
             return _rasterImage(surface, image->data, image->w, image->h, bbox);
         } else {
             if (translucent) {
-                if (isUpScaling) return _rasterTranslucentUpScaleImage(surface, image->data, image->w, image->h, opacity, bbox, &invTransform);
-                return _rasterTranslucentImage(surface, image->data, image->w, image->h, opacity, bbox, &invTransform);
+                if (fabsf(scaling - 1.0f) <= FLT_EPSILON) return _rasterTranslucentImage(surface, image->data, image->w, image->h, opacity, bbox, &invTransform);
+                else if (scaling < downScalingFactor) return _rasterTranslucentDownScaleImage(surface, image->data, image->w, image->h, opacity, bbox, &invTransform, scaling);
+                else return _rasterTranslucentUpScaleImage(surface, image->data, image->w, image->h, opacity, bbox, &invTransform);
             }
-            if (isUpScaling) return _rasterUpScaleImage(surface, image->data, image->w, image->h, bbox, &invTransform);
-            return _rasterImage(surface, image->data, image->w, image->h, bbox, &invTransform);
+            if (fabsf(scaling - 1.0f) <= FLT_EPSILON) return _rasterImage(surface, image->data, image->w, image->h, bbox, &invTransform);
+            else if (scaling  < downScalingFactor) return _rasterDownScaleImage(surface, image->data, image->w, image->h, bbox, &invTransform, scaling);
+            else return _rasterUpScaleImage(surface, image->data, image->w, image->h, bbox, &invTransform);
         }
     }
 }