GUACAMOLE-188: Use Porter-Duff "over" operator when drawing with ARGB surfaces.
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@ -279,14 +279,25 @@ void guac_common_surface_free(guac_common_surface* surface);
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void guac_common_surface_resize(guac_common_surface* surface, int w, int h);
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/**
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* Draws the given data to the given guac_common_surface.
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* Draws the given data to the given guac_common_surface. If the source surface
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* is ARGB, the draw operation will be performed using the Porter-Duff "over"
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* composite operator. If the source surface is RGB (no alpha channel), no
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* compositing is performed and destination pixels are ignored.
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*
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* @param surface The surface to draw to.
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* @param x The X coordinate of the draw location.
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* @param y The Y coordinate of the draw location.
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* @param src The Cairo surface to retrieve data from.
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* @param surface
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* The surface to draw to.
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*
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* @param x
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* The X coordinate of the draw location.
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*
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* @param y
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* The Y coordinate of the draw location.
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*
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* @param src
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* The Cairo surface to retrieve data from.
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*/
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void guac_common_surface_draw(guac_common_surface* surface, int x, int y, cairo_surface_t* src);
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void guac_common_surface_draw(guac_common_surface* surface, int x, int y,
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cairo_surface_t* src);
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/**
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* Paints to the given guac_common_surface using the given data as a stencil,
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@ -862,6 +862,75 @@ static void __guac_common_surface_set(guac_common_surface* dst,
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}
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/**
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* Applies the Porter-Duff "over" composite operator, blending the two given
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* color components using the given alpha value.
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*
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* @param dst
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* The destination color component.
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*
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* @param src
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* The source color component.
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*
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* @param alpha
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* The alpha value which applies to the blending operation.
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*
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* @return
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* The result of applying the Porter-Duff "over" composite operator to the
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* given source and destination components.
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*/
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static int guac_common_surface_blend_component(int dst, int src, int alpha) {
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return src + dst * (0xFF - alpha);
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}
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/**
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* Applies the Porter-Duff "over" composite operator, blending each component
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* of the two given ARGB colors.
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*
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* @param dst
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* The destination ARGB color.
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*
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* @param src
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* The source ARGB color.
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*
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* @return
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* The result of applying the Porter-Duff "over" composite operator to the
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* given source and destination colors.
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*/
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static uint32_t guac_common_surface_argb_blend(uint32_t dst, uint32_t src) {
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/* Separate destination ARGB color into its components */
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int dst_a = (dst >> 24) & 0xFF;
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int dst_r = (dst >> 16) & 0xFF;
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int dst_g = (dst >> 8) & 0xFF;
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int dst_b = dst & 0xFF;
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/* Separate source ARGB color into its components */
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int src_a = (src >> 24) & 0xFF;
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int src_r = (src >> 16) & 0xFF;
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int src_g = (src >> 8) & 0xFF;
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int src_b = src & 0xFF;
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/* If source is fully opaque (or destination is fully transparent), the
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* blended result is the source */
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if (src_a == 0xFF || dst_a == 0x00)
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return src;
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/* If source is fully transparent, the blended result is the destination */
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if (src_a == 0x00)
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return dst;
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/* Otherwise, blend each ARGB component, assuming pre-multiplied alpha */
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int r = guac_common_surface_blend_component(dst_r, src_r, src_a);
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int g = guac_common_surface_blend_component(dst_g, src_g, src_a);
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int b = guac_common_surface_blend_component(dst_b, src_b, src_a);
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int a = guac_common_surface_blend_component(dst_a, src_a, src_a);
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/* Recombine blended components */
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return (a << 24) | (r << 16) | (g << 8) | b;
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}
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/**
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* Copies data from the given buffer to the surface at the given coordinates.
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* The dimensions and location of the destination rectangle will be altered
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@ -906,22 +975,34 @@ static void __guac_common_surface_put(unsigned char* src_buffer, int src_stride,
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/* Copy row */
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for (x=0; x < rect->width; x++) {
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if (opaque || (*src_current & 0xFF000000)) {
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uint32_t color;
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uint32_t new_color = *src_current | 0xFF000000;
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uint32_t old_color = *dst_current;
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/* Get source and destination color values */
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uint32_t src_color = *src_current;
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uint32_t dst_color = *dst_current;
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if (old_color != new_color) {
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if (x < min_x) min_x = x;
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if (y < min_y) min_y = y;
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if (x > max_x) max_x = x;
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if (y > max_y) max_y = y;
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*dst_current = new_color;
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}
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/* Ignore alpha channel if opaque */
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if (opaque)
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color = src_color | 0xFF000000;
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/* Otherwise, perform alpha blending operation */
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else
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color = guac_common_surface_argb_blend(dst_color, src_color);
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/* If the destination color is changing, update rectangle bounds
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* and store the new color */
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if (dst_color != color) {
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if (x < min_x) min_x = x;
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if (y < min_y) min_y = y;
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if (x > max_x) max_x = x;
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if (y > max_y) max_y = y;
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*dst_current = color;
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}
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/* Advance to next pixel */
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src_current++;
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dst_current++;
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}
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/* Next row */
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