REDESIGNED: ImageDraw(), optimized #1218

After multiple tests and lot of redesign, current implementation is the fastest one. It also considers several fast-paths for maximum speed!

src/textures.c

@@ -2524,146 +2524,26 @@ void ImageDraw(Image *dst, Image src, Rectangle srcRec, Rectangle dstRec, Color
     if (dst->format >= COMPRESSED_DXT1_RGB) TRACELOG(LOG_WARNING, "Image drawing not supported for compressed formats");
     else
     {
-        // Despite all my efforts for optimization, original implementation is faster...
-        // I left here other implementations for future reference
-#define IMAGEDRAW_METHOD02
-#if defined(IMAGEDRAW_METHOD01)
-        // Security checks to avoid size and rectangle issues (out of bounds)
-        // Check that srcRec is inside src image
-        if (srcRec.x < 0) srcRec.x = 0;
-        if (srcRec.y < 0) srcRec.y = 0;
-
-        if ((srcRec.x + srcRec.width) > src.width)srcRec.width = src.width - srcRec.x;
-        if ((srcRec.y + srcRec.height) > src.height) srcRec.height = src.height - srcRec.y;
-        
-        Image srcMod = ImageCopy(src);     // Make a copy of source image to work with it
-
-        // Crop source image to desired source rectangle (if required)
-        if ((src.width != (int)srcRec.width) && (src.height != (int)srcRec.height)) 
-        {
-            ImageCrop(&srcMod, srcRec);
-        }
-
-        // Scale source image in case destination rec size is different than source rec size
-        if (((int)dstRec.width != (int)srcRec.width) || ((int)dstRec.height != (int)srcRec.height))
-        {
-            ImageResize(&srcMod, (int)dstRec.width, (int)dstRec.height);
-        }
-
-        // Check that dstRec is inside dst image
-        // Allow negative position within destination with cropping
-        if (dstRec.x < 0)
-        {
-            ImageCrop(&srcMod, (Rectangle) { -dstRec.x, 0, dstRec.width + dstRec.x, dstRec.height });
-            dstRec.width = dstRec.width + dstRec.x;
-            dstRec.x = 0;
-        }
-
-        if ((dstRec.x + dstRec.width) > dst->width)
-        {
-            ImageCrop(&srcMod, (Rectangle) { 0, 0, dst->width - dstRec.x, dstRec.height });
-            dstRec.width = dst->width - dstRec.x;
-        }
-
-        if (dstRec.y < 0)
-        {
-            ImageCrop(&srcMod, (Rectangle) { 0, -dstRec.y, dstRec.width, dstRec.height + dstRec.y });
-            dstRec.height = dstRec.height + dstRec.y;
-            dstRec.y = 0;
-        }
-
-        if ((dstRec.y + dstRec.height) > dst->height)
-        {
-            ImageCrop(&srcMod, (Rectangle) { 0, 0, dstRec.width, dst->height - dstRec.y });
-            dstRec.height = dst->height - dstRec.y;
-        }
-
-        // Get image data as Color pixels array to work with it
-        Color *dstPixels = GetImageData(*dst);
-        Color *srcPixels = GetImageData(srcMod);
-
-        UnloadImage(srcMod);       // Source copy not required any more
-
-        Vector4 fsrc, fdst, fout;   // Normalized pixel data (ready for operation)
-        Vector4 ftint = ColorNormalize(tint);   // Normalized color tint
-
-        // Blit pixels, copy source image into destination
-        for (int j = (int)dstRec.y; j < (int)(dstRec.y + dstRec.height); j++)
-        {
-            for (int i = (int)dstRec.x; i < (int)(dstRec.x + dstRec.width); i++)
-            {
-                // Alpha blending (https://en.wikipedia.org/wiki/Alpha_compositing)
-
-                fdst = ColorNormalize(dstPixels[j*(int)dst->width + i]);
-                fsrc = ColorNormalize(srcPixels[(j - (int)dstRec.y)*(int)dstRec.width + (i - (int)dstRec.x)]);
-
-                // Apply color tint to source image
-                fsrc.x *= ftint.x; fsrc.y *= ftint.y; fsrc.z *= ftint.z; fsrc.w *= ftint.w;
-
-                fout.w = fsrc.w + fdst.w*(1.0f - fsrc.w);
-
-                if (fout.w <= 0.0f)
-                {
-                    fout.x = 0.0f;
-                    fout.y = 0.0f;
-                    fout.z = 0.0f;
-                }
-                else
-                {
-                    fout.x = (fsrc.x*fsrc.w + fdst.x*fdst.w*(1 - fsrc.w))/fout.w;
-                    fout.y = (fsrc.y*fsrc.w + fdst.y*fdst.w*(1 - fsrc.w))/fout.w;
-                    fout.z = (fsrc.z*fsrc.w + fdst.z*fdst.w*(1 - fsrc.w))/fout.w;
-                }
-
-                dstPixels[j*(int)dst->width + i] = (Color){ (unsigned char)(fout.x*255.0f),
-                                                            (unsigned char)(fout.y*255.0f),
-                                                            (unsigned char)(fout.z*255.0f),
-                                                            (unsigned char)(fout.w*255.0f) };
-
-                // TODO: Support other blending options
-            }
-        }
-
-        Image final = {
-            .data = dstPixels,
-            .width = dst->width,
-            .height = dst->height,
-            .format = UNCOMPRESSED_R8G8B8A8,
-            .mipmaps = 1
-        };
-
-        // NOTE: dstPixels are free() inside ImageFormat()
-        ImageFormat(&final, dst->format);
-       
-        UnloadImage(*dst);
-        *dst = final;
-
-        RL_FREE(srcPixels);
-#endif
-#if defined(IMAGEDRAW_METHOD02)
-        Image srcMod = ImageCopy(src);                 // Make a copy of source image to work with it
-        ImageFormat(&srcMod, UNCOMPRESSED_R8G8B8A8);   // Convert to R8G8B8A8 to help on blending
+        Image srcMod = { 0 };       // Source copy (in case it was required)
+        Image *srcPtr = &src;       // Pointer to source image
+        bool useSrcMod = false;     // Track source copy required
 
         // Source rectangle out-of-bounds security checks
         if (srcRec.x < 0) { srcRec.width -= srcRec.x; srcRec.x = 0; }
         if (srcRec.y < 0) { srcRec.height -= srcRec.y; srcRec.y = 0; }
         if ((srcRec.x + srcRec.width) > src.width) srcRec.width = src.width - srcRec.x;
         if ((srcRec.y + srcRec.height) > src.height) srcRec.height = src.height - srcRec.y;
-        
+
         // Check if source rectangle needs to be resized to destination rectangle
         // In that case, we make a copy of source and we apply all required transform
-        if ((srcRec.width != fabs(dstRec.width - dstRec.x)) || (srcRec.height != fabs(dstRec.height - dstRec.y)))
+        if (((int)srcRec.width != (int)dstRec.width) || ((int)srcRec.height != (int)dstRec.height))
         {
-            ImageCrop(&srcMod, srcRec);        // Crop to source rectangle
+            srcMod = ImageFromImage(src, srcRec);   // Create image from another image
             ImageResize(&srcMod, (int)dstRec.width, (int)dstRec.height);   // Resize to destination rectangle
             srcRec = (Rectangle){ 0, 0, srcMod.width, srcMod.height };
-        }
-        
-        // Check if destination format is different than source format and no source copy created yet
-        if (dst->format != src.format)
-        {
-            ImageCrop(&srcMod, srcRec);        // Crop to source rectangle
-            srcRec = (Rectangle){ 0, 0, srcMod.width, srcMod.height };
+
+            srcPtr = &srcMod;
+            useSrcMod = true;
         }
 
         // Destination rectangle out-of-bounds security checks
@@ -2673,7 +2553,7 @@ void ImageDraw(Image *dst, Image src, Rectangle srcRec, Rectangle dstRec, Color
             srcRec.width += dstRec.x;
             dstRec.x = 0;
         }
-        else if ((dstRec.x + srcMod.width) > dst->width) srcRec.width = dst->width - dstRec.x;
+        else if ((dstRec.x + srcPtr->width) > dst->width) srcRec.width = dst->width - dstRec.x;
 
         if (dstRec.y < 0)
         {
@@ -2681,113 +2561,67 @@ void ImageDraw(Image *dst, Image src, Rectangle srcRec, Rectangle dstRec, Color
             srcRec.height += dstRec.y;
             dstRec.y = 0;
         }
-        else if ((dstRec.y + srcMod.height) > dst->height) srcRec.height = dst->height - dstRec.y;
+        else if ((dstRec.y + srcPtr->height) > dst->height) srcRec.height = dst->height - dstRec.y;
 
         if (dst->width < srcRec.width) srcRec.width = dst->width;
         if (dst->height < srcRec.height) srcRec.height = dst->height;
+
+        // This blitting method is quite fast! The process followed is:
+        // for every pixel -> [get_src_format/get_dst_format -> blend -> format_to_dst]
+        // Some optimization ideas:
+        //    [x] Avoid creating source copy if not required (no resize required)
+        //    [x] Optimize ImageResize() for pixel format (alternative: ImageResizeNN())
+        //    [x] Optimize ColorAlphaBlend() to avoid processing (alpha = 0) and (alpha = 1)
+        //    [x] Optimize ColorAlphaBlend() for faster operations (maybe avoiding divs?)
+        //    [x] Consider fast path: no alpha blending required cases (src has no alpha)
+        //    [x] Consider fast path: same src/dst format with no alpha -> direct line copy
+        //    [-] GetPixelColor(): Return Vector4 instead of Color, easier for ColorAlphaBlend()
+
+        Color colSrc, colDst, blend;
+        bool blendRequired = true;
         
-    #define IMAGEDRAW_NO_IMAGEFORMAT
-    #if defined(IMAGEDRAW_NO_BLENDING)
-        // This method is very fast but no pixels blending is considered
-        int dataSize = GetPixelDataSize(dst->width, dst->height, dst->format);
-        int bytesPerPixel = dataSize/(dst->width*dst->height);
-        
-        // Image blitting src -> destination, line by line
-        for (int y = 0; y < (int)srcRec.height; y++)
-        {
-            memcpy((unsigned char *)dst->data + ((int)dstRec.y*dst->width + (int)dstRec.x + y*dst->width)*bytesPerPixel, 
-                   (unsigned char *)srcMod.data + ((y + (int)srcRec.y)*srcMod.width + (int)srcRec.x)*bytesPerPixel,
-                   (int)srcRec.width*bytesPerPixel);
-        }
-    #endif
-    #if defined(IMAGEDRAW_IMAGEFORMAT)
-        // This method is slower than expected, it seems ImageFormat() to RGBA and back to original format,
-        // combined with alpha blending makes it quite slow
-
-        // Convert destination to R8G8B8A8 for blending calculation
-        int dstFormat = dst->format;
-        ImageFormat(dst, UNCOMPRESSED_R8G8B8A8);    // Force 4 bytes per pixel with alpha for blending
-        
-        Vector4 fsrc, fdst, fout;                   // Normalized pixel data (ready for operation)
-        Vector4 ftint = ColorNormalize(tint);       // Normalized color tint
-        unsigned char srcAlpha = 0;
+        // Fast path: Avoid blend if source has no alpha to blend
+        if ((tint.a == 255) && ((srcPtr->format == UNCOMPRESSED_GRAYSCALE) || (srcPtr->format == UNCOMPRESSED_R8G8B8) || (srcPtr->format == UNCOMPRESSED_R5G6B5))) blendRequired = false;       
 
-        for (int y = 0; y < (int)srcRec.height; y++)
-        {
-            for (int x = 0; x < (int)srcRec.width; x++)
-            {
-                srcAlpha = ((Color *)srcMod.data)[((y + (int)srcRec.y)*srcMod.width + (int)srcRec.x) + x].a;
-                
-                if (srcAlpha == 255)
-                {
-                    ((Color *)dst->data)[((int)dstRec.y*dst->width + (int)dstRec.x) + y*(dst->width) + x] = ((Color *)srcMod.data)[((y + (int)srcRec.y)*srcMod.width + (int)srcRec.x) + x];
-                }
-                else if (srcAlpha > 0)
-                {
-                    // Alpha blending (https://en.wikipedia.org/wiki/Alpha_compositing)
+        int strideDst = GetPixelDataSize(dst->width, 1, dst->format);
+        int bytesPerPixelDst = strideDst/(dst->width);
 
-                    fdst = ColorNormalize(((Color *)dst->data)[((int)dstRec.y*dst->width + (int)dstRec.x) + y*(dst->width) + x]);
-                    fsrc = ColorNormalize(((Color *)srcMod.data)[((y + (int)srcRec.y)*srcMod.width + (int)srcRec.x) + x]);
+        int strideSrc = GetPixelDataSize(srcPtr->width, 1, srcPtr->format);
+        int bytesPerPixelSrc = strideSrc/(srcPtr->width);
 
-                    // Apply color tint to source image
-                    fsrc.x *= ftint.x; fsrc.y *= ftint.y; fsrc.z *= ftint.z; fsrc.w *= ftint.w;
+        unsigned char *pSrcBase = (unsigned char *)srcPtr->data + ((int)srcRec.y*srcPtr->width + (int)srcRec.x)*bytesPerPixelSrc;
+        unsigned char *pDstBase = (unsigned char *)dst->data + ((int)dstRec.y*dst->width + (int)dstRec.x)*bytesPerPixelDst;
 
-                    fout.w = fsrc.w + fdst.w*(1.0f - fsrc.w);
+        for (int y = 0; y < (int)srcRec.height; y++)
+        {
+            unsigned char *pSrc = pSrcBase;
+            unsigned char *pDst = pDstBase;
 
-                    if (fout.w <= 0.0f)
-                    {
-                        fout.x = 0.0f;
-                        fout.y = 0.0f;
-                        fout.z = 0.0f;
-                    }
-                    else
-                    {
-                        fout.x = (fsrc.x*fsrc.w + fdst.x*fdst.w*(1 - fsrc.w))/fout.w;
-                        fout.y = (fsrc.y*fsrc.w + fdst.y*fdst.w*(1 - fsrc.w))/fout.w;
-                        fout.z = (fsrc.z*fsrc.w + fdst.z*fdst.w*(1 - fsrc.w))/fout.w;
-                    }
+            // Fast path: Avoid moving pixel by pixel if no blend required and same format
+            if (!blendRequired && (srcPtr->format == dst->format)) memcpy(pDst, pSrc, srcRec.width*bytesPerPixelSrc);
+            else
+            {
+                for (int x = 0; x < (int)srcRec.width; x++)
+                {
+                    colSrc = GetPixelColor(pSrc, srcPtr->format);
+                    colDst = GetPixelColor(pDst, dst->format);
+                    
+                    // Fast path: Avoid blend if source has no alpha to blend
+                    if (blendRequired) blend = ColorAlphaBlend(colDst, colSrc, tint);
+                    else blend = colSrc;
 
-                    ((Color *)dst->data)[((int)dstRec.y*dst->width + (int)dstRec.x) + y*(dst->width) + x] = (Color){ (unsigned char)(fout.x*255.0f), (unsigned char)(fout.y*255.0f), (unsigned char)(fout.z*255.0f), (unsigned char)(fout.w*255.0f) };
+                    SetPixelColor(pDst, blend, dst->format);
 
-                    // TODO: Support other blending options
+                    pDst += bytesPerPixelDst;
+                    pSrc += bytesPerPixelSrc;
                 }
             }
-        }
-        
-        ImageFormat(dst, dstFormat);    // Restore original image format after drawing with blending
-        UnloadImage(srcMod);            // Unload source modified image
-    #endif
-    #if defined(IMAGEDRAW_NO_IMAGEFORMAT)
-        // This new method is quite fast, it seems it gets the best results! 
-        // It [formats_src -> blend -> format_dst] per pixel! and it can be further optimized!
-        // Some ideas:
-        //    - Optimize ColorAlphaBlend() to avoid processing (alpha = 0) and (alpha = 1)
-        //    - Optimize ColorAlphaBlend() for faster operations (maybe avoiding divs?)
-        //    - GetPixelColor(): Return Vector4 instead of Color, easier for ColorAlphaBlend()
-        //    - Consider special src/dst format cases when there is no alpha -> [formats_src -> format_dst]
-        Color psrc, pdst, blend;
-        
-        int dataSizeDst = GetPixelDataSize(dst->width, dst->height, dst->format);
-        int bytesPerPixelDst = dataSizeDst/(dst->width*dst->height);
-        
-        int dataSizeSrc = GetPixelDataSize(srcMod.width, srcMod.height, srcMod.format);
-        int bytesPerPixelSrc = dataSizeSrc/(srcMod.width*srcMod.height);
-    
-        for (int y = 0; y < (int)srcRec.height; y++)
-        {
-            for (int x = 0; x < (int)srcRec.width; x++)
-            {
-                psrc = GetPixelColor((unsigned char *)srcMod.data + (((y + (int)srcRec.y)*srcMod.width + (int)srcRec.x) + x)*bytesPerPixelSrc, srcMod.format);
-                pdst = GetPixelColor((unsigned char *)dst->data + (((int)dstRec.y*dst->width + (int)dstRec.x) + y*(dst->width) + x)*bytesPerPixelDst, dst->format);
-                blend = ColorAlphaBlend(pdst, psrc, tint);
-                
-                ColorWrite((unsigned char *)dst->data + (((int)dstRec.y*dst->width + (int)dstRec.x) + y*(dst->width) + x)*bytesPerPixelDst, blend, dst->format);
-            }
+
+            pSrcBase += strideSrc;
+            pDstBase += strideDst;
         }
 
-        UnloadImage(srcMod);            // Unload source modified image
-    #endif
-#endif
+        if (useSrcMod) UnloadImage(srcMod);     // Unload source modified image
     }
 }