Use pre-multiplied colors by default

wlr_scene_rects expect their color to be pre-multiplied
while cairo_set_source_rgba() expects them to not be
pre-multiplied. With this patch we now use premultiplied
colors internally by default and then reverse it when
setting cairo colors.

This ensures the titlebar uses a consistent color in case
it was defined with some transparency by the user.

Fixes: #1684

diff --git a/src/common/graphic-helpers.c b/src/common/graphic-helpers.c
index 460b6760dade8c2cb8d275dc89b1bc2bb6baaca2..055b0635b6b11bb22e012532f9482fe0a168cfc3 100644 (file)
--- a/src/common/graphic-helpers.c
+++ b/src/common/graphic-helpers.c
@@ -85,7 +85,19 @@ draw_cairo_border(cairo_t *cairo, struct wlr_fbox fbox, double line_width)
 void
 set_cairo_color(cairo_t *cairo, const float *c)
 {
-       cairo_set_source_rgba(cairo, c[0], c[1], c[2], c[3]);
+       /*
+        * We are dealing with pre-multiplied colors
+        * but cairo expects unmultiplied colors here
+        */
+       float alpha = c[3];
+
+       if (alpha == 0.0f) {
+               cairo_set_source_rgba(cairo, 0, 0, 0, 0);
+               return;
+       }
+
+       cairo_set_source_rgba(cairo, c[0] / alpha, c[1] / alpha,
+               c[2] / alpha, alpha);
 }
 
 struct surface_context

diff --git a/src/overlay.c b/src/overlay.c
index 04471b50329e7984ed43765c34531628f1883e20..aaed41d2381be96948da1b606140a3ad66c7ff07 100644 (file)
--- a/src/overlay.c
+++ b/src/overlay.c
@@ -16,7 +16,7 @@ create_overlay(struct seat *seat)
        seat->overlay.tree = parent;
        wlr_scene_node_set_enabled(&parent->node, false);
        if (!wlr_renderer_is_pixman(server->renderer)) {
-               /* Hardware assisted rendering: Half transparent overlay */
+               /* Hardware assisted rendering: Half transparent overlay, pre-multiplied */
                float color[4] = { 0.25, 0.25, 0.35, 0.5 };
                seat->overlay.rect = wlr_scene_rect_create(parent, 0, 0, color);
        } else {

diff --git a/src/theme.c b/src/theme.c
index 8ad93384685ebe7520bea8eff4b2145b851dd279..983d7bc4d92fe21266bdd1318337a07e28ecc396 100644 (file)
--- a/src/theme.c
+++ b/src/theme.c
@@ -135,8 +135,8 @@ create_hover_fallback(struct theme *theme, const char *icon_name,
                (width - icon_width) / 2, (height - icon_height) / 2);
        cairo_paint(cairo);
 
-       /* Overlay (non-multiplied alpha) */
-       float overlay_color[4] = { 0.5f, 0.5f, 0.5f, 0.3f};
+       /* Overlay (pre-multiplied alpha) */
+       float overlay_color[4] = { 0.15f, 0.15f, 0.15f, 0.3f};
        enum corner corner = corner_from_icon_name(icon_name);
 
        if (corner == LAB_CORNER_UNKNOWN) {
@@ -406,6 +406,10 @@ parse_hexstr(const char *hex, float *rgba)
        rgba[2] = (hex_to_dec(hex[5]) * 16 + hex_to_dec(hex[6])) / 255.0;
        if (strlen(hex) > 7) {
                rgba[3] = atoi(hex + 7) / 100.0;
+               /* Pre-multiply everything as expected by wlr_scene */
+               rgba[0] *= rgba[3];
+               rgba[1] *= rgba[3];
+               rgba[2] *= rgba[3];
        } else {
                rgba[3] = 1.0;
        }