Make background_image tint useable even without a background image in a transparent window

docs/changelog.rst

@@ -13,6 +13,9 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
 - Add support for specifying a background image, see :opt:`background_image`
   (:iss:`163` and :pull:`2326`)
 
+- A new :opt:`background_tint` option to darken the background under the text
+  area when using background images and/or transparent windows.
+
 
 
 0.16.0 [2020-01-28]

kitty/config_data.py

@@ -864,12 +864,6 @@ Path to a background image. Must be in PNG format.'''))
 o('background_image_layout', 'tiled', option_type=choices('tiled', 'scaled', 'mirror-tiled'), long_text=_('''
 Whether to tile or scale the background image.'''))
 
-o('background_image_tint', 0.5, option_type=unit_float, long_text=_('''
-How much to tint the background image by the background area. The tint is applied
-only under the text area, not margin/borders. Makes it easier to read the text.
-Tinting is done using the current background color for each window.
-'''))
-
 o('background_image_linear', False, long_text=_('''
 When background image is scaled, whether linear interpolation should be used.'''))
 
@@ -879,6 +873,14 @@ shortcuts (:sc:`increase_background_opacity` and :sc:`decrease_background_opacit
 or the remote control facility.
 '''))
 
+o('background_tint', 0.0, option_type=unit_float, long_text=_('''
+How much to tint the background image by the background color. The tint is applied
+only under the text area, not margin/borders. Makes it easier to read the text.
+Tinting is done using the current background color for each window. This setting
+applies only if :opt:`background_opacity` is set and transparent windows are supported
+or :opt:`background_image` is set.
+'''))
+
 o('dim_opacity', 0.75, option_type=unit_float, long_text=_('''
 How much to dim text that has the DIM/FAINT attribute set. One means no dimming and
 zero means fully dimmed (i.e. invisible).'''))

kitty/shaders.c

@@ -446,7 +446,7 @@ draw_tint(bool premult, Screen *screen, GLfloat xstart, GLfloat ystart, GLfloat
     bind_program(TINT_PROGRAM);
     color_type window_bg = colorprofile_to_color(screen->color_profile, screen->color_profile->overridden.default_bg, screen->color_profile->configured.default_bg);
 #define C(shift) ((((GLfloat)((window_bg >> shift) & 0xFF)) / 255.0f))
-    float alpha = OPT(background_image_tint);
+    float alpha = OPT(background_tint);
     if (premult) glUniform4f(tint_program_layout.tint_color_location, C(16) * alpha, C(8) * alpha, C(0) * alpha, alpha);
     else glUniform4f(tint_program_layout.tint_color_location, C(16), C(8), C(0), alpha);
 #undef C
@@ -464,7 +464,7 @@ draw_cells_interleaved(ssize_t vao_idx, ssize_t gvao_idx, Screen *screen, OSWind
         bind_program(CELL_BG_PROGRAM);
         glUniform1ui(cell_program_layouts[CELL_BG_PROGRAM].draw_bg_bitfield_location, 3);
         glDrawArraysInstanced(GL_TRIANGLE_FAN, 0, 4, screen->lines * screen->columns);
-    } else if (OPT(background_image_tint) > 0) draw_tint(false, screen, xstart, ystart, width, height);
+    } else if (OPT(background_tint) > 0) draw_tint(false, screen, xstart, ystart, width, height);
 
     if (screen->grman->num_of_below_refs || has_bgimage(w)) {
         if (screen->grman->num_of_below_refs) draw_graphics(
@@ -490,7 +490,7 @@ draw_cells_interleaved(ssize_t vao_idx, ssize_t gvao_idx, Screen *screen, OSWind
 
 static void
 draw_cells_interleaved_premult(ssize_t vao_idx, ssize_t gvao_idx, Screen *screen, OSWindow *os_window, GLfloat xstart, GLfloat ystart, GLfloat width, GLfloat height) {
-    if (has_bgimage(os_window) && OPT(background_image_tint) > 0.f) {
+    if (OPT(background_tint) > 0.f) {
         glEnable(GL_BLEND);
         BLEND_PREMULT;
         draw_tint(true, screen, xstart, ystart, width, height);

kitty/state.c

@@ -560,7 +560,7 @@ PYWRAP1(set_options) {
     S(cursor_stop_blinking_after, parse_s_double_to_monotonic_t);
     S(background_opacity, PyFloat_AsFloat);
     S(background_image_layout, bglayout);
-    S(background_image_tint, PyFloat_AsFloat);
+    S(background_tint, PyFloat_AsFloat);
     S(background_image_linear, PyObject_IsTrue);
     S(dim_opacity, PyFloat_AsFloat);
     S(dynamic_background_opacity, PyObject_IsTrue);

kitty/state.h

@@ -42,7 +42,7 @@ typedef struct {
     char* background_image;
     BackgroundImageLayout background_image_layout;
     bool background_image_linear;
-    float background_image_tint;
+    float background_tint;
 
     bool dynamic_background_opacity;
     float inactive_text_alpha;