From 8e7b8b70dc5f98e82f62536deaea22f351b7b63e Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Fri, 31 Jan 2020 11:34:34 +0530
Subject: [PATCH] A VAO is not needed to draw background images

---
 kitty/bgimage_fragment.glsl |  9 ++++-----
 kitty/bgimage_vertex.glsl   | 18 +++++++++++++++---
 kitty/shaders.c             | 35 +++++++----------------------------
 kitty/state.h               |  3 +--
 4 files changed, 27 insertions(+), 38 deletions(-)

diff --git a/kitty/bgimage_fragment.glsl b/kitty/bgimage_fragment.glsl
index d8a6d4c14..7256b0157 100644
--- a/kitty/bgimage_fragment.glsl
+++ b/kitty/bgimage_fragment.glsl
@@ -6,17 +6,16 @@ uniform float bgimage_opacity;
 #ifdef TILED
 uniform float bgimage_scale;
 
-// These are of the window, not the screen.
-uniform float width;
-uniform float height;
+uniform float window_width;
+uniform float window_height;
 #endif
 in vec2 texcoord;
 out vec4 color;
 
 void main() {
 #ifdef TILED
-    vec2 txsz = vec2(width,height) / textureSize(image,0);
-    txsz /= bgimage_scale;
+    ivec2 image_size = textureSize(image, 0);
+    vec2 txsz = vec2(window_width / (float(image_size[0]) * bgimage_scale), window_height / (float(image_size[1]) * bgimage_scale));
     color = texture(image, texcoord * txsz);
 #endif
 #ifdef SIMPLE
diff --git a/kitty/bgimage_vertex.glsl b/kitty/bgimage_vertex.glsl
index a53d8b320..d28176a81 100644
--- a/kitty/bgimage_vertex.glsl
+++ b/kitty/bgimage_vertex.glsl
@@ -1,9 +1,21 @@
 #version GLSL_VERSION
+#define left  -1.0f
+#define top  1.0f
+#define right  1.0f
+#define bottom  -1.0f
 
-layout(location=0) in vec4 src;
 out vec2 texcoord;
 
+const vec2 pos_map[] = vec2[4](
+    vec2(left, top),
+    vec2(left, bottom),
+    vec2(right, bottom),
+    vec2(right, top)
+);
+
+
 void main() {
-    texcoord = clamp(vec2(src[0], src[1]*-1), 0, 1);
-    gl_Position = src;
+    vec2 vertex = pos_map[gl_VertexID];
+    texcoord = clamp(vec2(vertex[0], vertex[1]*-1), 0, 1);
+    gl_Position = vec4(vertex, 0, 1);
 }
diff --git a/kitty/shaders.c b/kitty/shaders.c
index 72f46ab7a..21e40a001 100644
--- a/kitty/shaders.c
+++ b/kitty/shaders.c
@@ -334,28 +334,11 @@ cell_prepare_to_render(ssize_t vao_idx, ssize_t gvao_idx, Screen *screen, GLfloa
 
 static void
 draw_bg(int program, OSWindow *w) {
-    if (w->bvao_idx == 0) {
-        const GLfloat screenrect[4][2] = {
-            { -1.0,  1.0  },
-            { -1.0, -1.0  },
-            {  1.0, -1.0  },
-            {  1.0, 1.0  },
-        };
-        w->bvao_idx = create_vao();
-        bind_vertex_array(w->bvao_idx);
-        glGenBuffers(1, &w->vbo_idx);
-        glBindBuffer(GL_ARRAY_BUFFER, w->vbo_idx);
-        glBufferData(GL_ARRAY_BUFFER, sizeof(screenrect), screenrect, GL_STATIC_DRAW);
-    }
-    bind_vertex_array(w->bvao_idx);
-    glBindBuffer(GL_ARRAY_BUFFER, w->vbo_idx);
-
     glClear(GL_COLOR_BUFFER_BIT);
-    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 0, 0);
-    glEnableVertexAttribArray(0);
-
     bind_program(program);
-    static bool bgimage_constants_set;
+    bind_vertex_array(blit_vertex_array);
+
+    static bool bgimage_constants_set = false;
     if (!bgimage_constants_set) {
         glUniform1i(glGetUniformLocation(program_id(program), "image"), BGIMAGE_UNIT);
         glUniform1f(glGetUniformLocation(program_id(program), "bgimage_scale"), OPT(background_image_scale));
@@ -658,15 +641,11 @@ create_border_vao(void) {
 
 void
 draw_borders(ssize_t vao_idx, unsigned int num_border_rects, BorderRect *rect_buf, bool rect_data_is_dirty, uint32_t viewport_width, uint32_t viewport_height, color_type active_window_bg, unsigned int num_visible_windows, bool all_windows_have_same_bg, OSWindow *w) {
-    glEnable(GL_BLEND);
-    BLEND_ONTO_OPAQUE;
 
     if (w->bgimage != NULL) {
-        int program;
-        if (OPT(background_image_layout) == TILING || OPT(background_image_layout) == MIRRORED) program = BGIMAGE_TILED_PROGRAM;
-        else program = BGIMAGE_PROGRAM;
-
-        draw_bg(program, w);
+        glEnable(GL_BLEND);
+        BLEND_ONTO_OPAQUE;
+        draw_bg((OPT(background_image_layout) == TILING || OPT(background_image_layout) == MIRRORED) ? BGIMAGE_TILED_PROGRAM : BGIMAGE_PROGRAM, w);
     }
 
     if (num_border_rects) {
@@ -691,7 +670,7 @@ draw_borders(ssize_t vao_idx, unsigned int num_border_rects, BorderRect *rect_bu
         unbind_vertex_array();
         unbind_program();
     }
-    glDisable(GL_BLEND);
+    if (w->bgimage != NULL) glDisable(GL_BLEND);
 }
 
 // }}}
diff --git a/kitty/state.h b/kitty/state.h
index 3fb3952de..9cb43c104 100644
--- a/kitty/state.h
+++ b/kitty/state.h
@@ -169,8 +169,7 @@ typedef struct {
     monotonic_t last_render_frame_received_at;
     uint64_t render_calls;
     id_type last_focused_counter;
-    ssize_t gvao_idx, bvao_idx;
-    unsigned int vbo_idx;
+    ssize_t gvao_idx;
 } OSWindow;