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GUACAMOLE-188: Use Porter-Duff "over" operator when drawing with ARGB surfaces.

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This commit is contained in:
Michael Jumper 2017-02-25 16:13:56 -08:00
parent 4da4ce7279
commit 12d29569a6
2 changed files with 108 additions and 16 deletions
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23
src/common/common/surface.h
View File

@ -279,14 +279,25 @@ void guac_common_surface_free(guac_common_surface* surface);
void guac_common_surface_resize(guac_common_surface* surface, int w, int h);
/**
* Draws the given data to the given guac_common_surface.
* Draws the given data to the given guac_common_surface. If the source surface
* is ARGB, the draw operation will be performed using the Porter-Duff "over"
* composite operator. If the source surface is RGB (no alpha channel), no
* compositing is performed and destination pixels are ignored.
*
* @param surface The surface to draw to.
* @param x The X coordinate of the draw location.
* @param y The Y coordinate of the draw location.
* @param src The Cairo surface to retrieve data from.
* @param surface
* The surface to draw to.
*
* @param x
* The X coordinate of the draw location.
*
* @param y
* The Y coordinate of the draw location.
*
* @param src
* The Cairo surface to retrieve data from.
*/
void guac_common_surface_draw(guac_common_surface* surface, int x, int y, cairo_surface_t* src);
void guac_common_surface_draw(guac_common_surface* surface, int x, int y,
cairo_surface_t* src);
/**
* Paints to the given guac_common_surface using the given data as a stencil,

93
src/common/surface.c
View File

@ -862,6 +862,75 @@ static void __guac_common_surface_set(guac_common_surface* dst,
}
/**
* Applies the Porter-Duff "over" composite operator, blending the two given
* color components using the given alpha value.
*
* @param dst
* The destination color component.
*
* @param src
* The source color component.
*
* @param alpha
* The alpha value which applies to the blending operation.
*
* @return
* The result of applying the Porter-Duff "over" composite operator to the
* given source and destination components.
*/
static int guac_common_surface_blend_component(int dst, int src, int alpha) {
return src + dst * (0xFF - alpha);
}
/**
* Applies the Porter-Duff "over" composite operator, blending each component
* of the two given ARGB colors.
*
* @param dst
* The destination ARGB color.
*
* @param src
* The source ARGB color.
*
* @return
* The result of applying the Porter-Duff "over" composite operator to the
* given source and destination colors.
*/
static uint32_t guac_common_surface_argb_blend(uint32_t dst, uint32_t src) {
/* Separate destination ARGB color into its components */
int dst_a = (dst >> 24) & 0xFF;
int dst_r = (dst >> 16) & 0xFF;
int dst_g = (dst >> 8) & 0xFF;
int dst_b = dst & 0xFF;
/* Separate source ARGB color into its components */
int src_a = (src >> 24) & 0xFF;
int src_r = (src >> 16) & 0xFF;
int src_g = (src >> 8) & 0xFF;
int src_b = src & 0xFF;
/* If source is fully opaque (or destination is fully transparent), the
* blended result is the source */
if (src_a == 0xFF || dst_a == 0x00)
return src;
/* If source is fully transparent, the blended result is the destination */
if (src_a == 0x00)
return dst;
/* Otherwise, blend each ARGB component, assuming pre-multiplied alpha */
int r = guac_common_surface_blend_component(dst_r, src_r, src_a);
int g = guac_common_surface_blend_component(dst_g, src_g, src_a);
int b = guac_common_surface_blend_component(dst_b, src_b, src_a);
int a = guac_common_surface_blend_component(dst_a, src_a, src_a);
/* Recombine blended components */
return (a << 24) | (r << 16) | (g << 8) | b;
}
/**
* Copies data from the given buffer to the surface at the given coordinates.
* The dimensions and location of the destination rectangle will be altered
@ -906,22 +975,34 @@ static void __guac_common_surface_put(unsigned char* src_buffer, int src_stride,
/* Copy row */
for (x=0; x < rect->width; x++) {
if (opaque || (*src_current & 0xFF000000)) {
uint32_t color;
uint32_t new_color = *src_current | 0xFF000000;
uint32_t old_color = *dst_current;
/* Get source and destination color values */
uint32_t src_color = *src_current;
uint32_t dst_color = *dst_current;
if (old_color != new_color) {
/* Ignore alpha channel if opaque */
if (opaque)
color = src_color | 0xFF000000;
/* Otherwise, perform alpha blending operation */
else
color = guac_common_surface_argb_blend(dst_color, src_color);
/* If the destination color is changing, update rectangle bounds
* and store the new color */
if (dst_color != color) {
if (x < min_x) min_x = x;
if (y < min_y) min_y = y;
if (x > max_x) max_x = x;
if (y > max_y) max_y = y;
*dst_current = new_color;
}
*dst_current = color;
}
/* Advance to next pixel */
src_current++;
dst_current++;
}
/* Next row */