Prepare of alpha blending of cursor

Will allow for cursor blink animation eventually.

kitty/cell_fragment.glsl

@@ -16,7 +16,7 @@ in vec3 underline_pos;
 in vec3 cursor_pos;
 in vec3 strike_pos;
 in vec3 foreground;
-in vec4 cursor_color_vec;
+in vec4 cursor_color_premult;
 in vec3 decoration_fg;
 in float colored_sprite;
 #endif
@@ -134,7 +134,7 @@ vec4 calculate_premul_foreground_from_sprites(vec4 text_fg) {
     float combined_alpha = min(text_fg.a + strike_alpha, 1.0f);
     // Underline color might be different, so alpha blend
     vec4 ans = alpha_blend(vec4(text_fg.rgb, combined_alpha * effective_text_alpha), vec4(decoration_fg, underline_alpha * effective_text_alpha));
-    return mix(ans, cursor_color_vec, cursor_alpha);
+    return mix(ans, cursor_color_premult, cursor_alpha);
 }
 
 vec4 adjust_foreground_contrast_with_background(vec4 text_fg, vec3 bg) {

kitty/cell_vertex.glsl

@@ -9,7 +9,7 @@ layout(std140) uniform CellRenderData {
     uint default_fg, default_bg, highlight_fg, highlight_bg, cursor_fg, cursor_bg, url_color, url_style, inverted;
 
     uint xnum, ynum, cursor_fg_sprite_idx;
-    float cursor_x, cursor_y, cursor_w;
+    float cursor_x, cursor_y, cursor_w, cursor_opacity;
 
     uint color_table[NUM_COLORS + MARK_MASK + MARK_MASK + 2];
 };
@@ -44,7 +44,7 @@ uniform float dim_opacity;
 out vec3 sprite_pos;
 out vec3 underline_pos;
 out vec3 cursor_pos;
-out vec4 cursor_color_vec;
+out vec4 cursor_color_premult;
 out vec3 strike_pos;
 out vec3 foreground;
 out vec3 decoration_fg;
@@ -185,7 +185,7 @@ void main() {
     strike_pos = to_sprite_pos(cell_data.pos, ((text_attrs >> STRIKE_SHIFT) & ONE) * STRIKE_SPRITE_INDEX, ZERO, ZERO);
 
     // Cursor
-    cursor_color_vec = vec4(color_to_vec(cursor_bg), 1.0);
+    cursor_color_premult = vec4(color_to_vec(cursor_bg) * cursor_opacity, cursor_opacity);
     vec3 final_cursor_text_color = color_to_vec(cursor_fg);
     foreground = choose_color(cell_data.has_block_cursor, final_cursor_text_color, foreground);
     decoration_fg = choose_color(cell_data.has_block_cursor, final_cursor_text_color, decoration_fg);
@@ -222,7 +222,7 @@ void main() {
 
     // Selection and cursor
     bg = choose_color(float(is_selected & ONE), choose_color(use_cell_for_selection_bg, color_to_vec(fg_as_uint), color_to_vec(highlight_bg)), bg);
-    background = choose_color(cell_data.has_block_cursor, color_to_vec(cursor_bg), bg);
+    background = choose_color(cell_data.has_block_cursor, mix(bg, color_to_vec(cursor_bg), cursor_opacity), bg);
 #if !defined(TRANSPARENT) && (PHASE == PHASE_SPECIAL)
     float is_special_cell = cell_data.has_block_cursor + float(is_selected & ONE);
     bg_alpha = step(0.5, is_special_cell);

kitty/child-monitor.c

@@ -652,7 +652,7 @@ pyset_iutf8(ChildMonitor *self, PyObject *args) {
 static bool
 cursor_needs_render(Window *w) {
 #define cri w->render_data.screen->cursor_render_info
-    return w->cursor_visible_at_last_render != cri.is_visible || w->render_data.screen->last_rendered.cursor_x != cri.x || w->render_data.screen->last_rendered.cursor_y != cri.y || w->last_cursor_shape != cri.shape;
+    return w->cursor_opacity_at_last_render != cri.opacity || w->render_data.screen->last_rendered.cursor_x != cri.x || w->render_data.screen->last_rendered.cursor_y != cri.y || w->last_cursor_shape != cri.shape;
 #undef cri
 }
 
@@ -669,7 +669,7 @@ collect_cursor_info(CursorRenderInfo *ans, Window *w, monotonic_t now, OSWindow
         cursor = rd->screen->paused_rendering.expires_at ? &rd->screen->paused_rendering.cursor : rd->screen->cursor;
         ans->x = cursor->x; ans->y = cursor->y;
     }
-    ans->is_visible = false;
+    ans->opacity = 0;
     if (rd->screen->scrolled_by || !screen_is_cursor_visible(rd->screen)) return cursor_needs_render(w);
     monotonic_t time_since_start_blink = now - os_window->cursor_blink_zero_time;
     bool cursor_blinking = OPT(cursor_blink_interval) > 0 && !cursor->non_blinking && os_window->is_focused && (OPT(cursor_stop_blinking_after) == 0 || time_since_start_blink <= OPT(cursor_stop_blinking_after));
@@ -683,8 +683,8 @@ collect_cursor_info(CursorRenderInfo *ans, Window *w, monotonic_t now, OSWindow
         monotonic_t delay = bucket - time_since_start_blink;
         set_maximum_wait(delay);
     }
-    if (!do_draw_cursor) { ans->is_visible = false; return cursor_needs_render(w); }
-    ans->is_visible = true;
+    if (!do_draw_cursor) { ans->opacity = 0; return cursor_needs_render(w); }
+    ans->opacity = 1;
     ans->shape = cursor->shape ? cursor->shape : OPT(cursor_shape);
     ans->is_focused = os_window->is_focused;
     return cursor_needs_render(w);
@@ -752,7 +752,7 @@ prepare_to_render_os_window(OSWindow *os_window, monotonic_t now, unsigned int *
                     if (collect_cursor_info(&WD.screen->cursor_render_info, w, now, os_window)) needs_render = true;
                     WD.screen->cursor_render_info.is_focused = false;
                 } else {
-                    WD.screen->cursor_render_info.is_visible = false;
+                    WD.screen->cursor_render_info.opacity = 0;
                 }
             }
             if (scan_for_animated_images) {
@@ -803,7 +803,7 @@ render_prepared_os_window(OSWindow *os_window, unsigned int active_window_id, co
             if (WD.screen->start_visual_bell_at != 0) {
                 set_maximum_wait(OPT(repaint_delay));
             }
-            w->cursor_visible_at_last_render = WD.screen->cursor_render_info.is_visible; w->last_cursor_shape = WD.screen->cursor_render_info.shape;
+            w->cursor_opacity_at_last_render = WD.screen->cursor_render_info.opacity; w->last_cursor_shape = WD.screen->cursor_render_info.shape;
         }
     }
     if (os_window->live_resize.in_progress) draw_resizing_text(os_window);

kitty/data-types.h

@@ -300,9 +300,10 @@ typedef struct {
 } Cursor;
 
 typedef struct {
-    bool is_visible, is_focused, render_even_when_unfocused;
+    bool is_focused, render_even_when_unfocused;
     CursorShape shape;
     unsigned int x, y;
+    float opacity;
 } CursorRenderInfo;
 
 typedef enum DynamicColorType {

kitty/shaders.c

@@ -297,7 +297,7 @@ cell_update_uniform_block(ssize_t vao_idx, Screen *screen, int uniform_buffer, c
         GLuint default_fg, default_bg, highlight_fg, highlight_bg, cursor_fg, cursor_bg, url_color, url_style, inverted;
 
         GLuint xnum, ynum, cursor_fg_sprite_idx;
-        GLfloat cursor_x, cursor_y, cursor_w;
+        GLfloat cursor_x, cursor_y, cursor_w, cursor_opacity;
     };
     // Send the uniform data
     struct GPUCellRenderData *rd = (struct GPUCellRenderData*)map_vao_buffer(vao_idx, uniform_buffer, GL_WRITE_ONLY);
@@ -322,8 +322,9 @@ cell_update_uniform_block(ssize_t vao_idx, Screen *screen, int uniform_buffer, c
     // Cursor position
     enum { BLOCK_IDX = 0, BEAM_IDX = NUM_UNDERLINE_STYLES + 3, UNDERLINE_IDX = NUM_UNDERLINE_STYLES + 4, UNFOCUSED_IDX = NUM_UNDERLINE_STYLES + 5 };
     Line *line_for_cursor = NULL;
-    if (cursor->is_visible) {
+    if (cursor->opacity > 0) {
         rd->cursor_x = cursor->x, rd->cursor_y = cursor->y;
+        rd->cursor_opacity = cursor->opacity;
         if (cursor->is_focused) {
             switch(cursor->shape) {
                 default:

kitty/state.h

@@ -178,7 +178,8 @@ typedef struct WindowBarData {
 
 typedef struct {
     id_type id;
-    bool visible, cursor_visible_at_last_render;
+    bool visible;
+    float cursor_opacity_at_last_render;
     CursorShape last_cursor_shape;
     PyObject *title;
     WindowRenderData render_data;