Added glyph rendering using stb_truetype

glyph/shaders/font_frag.glsl

@@ -0,0 +1,52 @@
+#version 450 core
+#extension GL_ARB_texture_rectangle: enable
+
+layout(location=1) uniform uint coverage_adjustment;
+layout(location=2) uniform uint  front_index; //gap buffer front
+
+layout(binding  = 0) uniform sampler2DRect glyph_atlas;
+
+in vec2 tex_coords;
+in flat vec4 color;
+in flat float subpixel_shift;
+in flat uint index_out;
+
+
+layout(location = 0, index = 0) out vec4 fragment_color;
+layout(location = 0, index = 1) out vec4 blend_weights;
+
+void main (){
+
+
+
+    vec3 current  = texelFetch(glyph_atlas, ivec2(tex_coords) + ivec2( 0, 0)).rgb;
+    vec3 previous = texelFetch(glyph_atlas, ivec2(tex_coords) + ivec2(-1, 0)).rgb;
+    float r = current.r, g = current.g, b = current.b;
+    if (subpixel_shift <= 1.0/3.0) {
+      float z = 3.0 * subpixel_shift;
+      r = mix(current.r, previous.b, z);
+      g = mix(current.g, current.r, z);
+      b = mix(current.b, current.g, z);
+    } else if (subpixel_shift <= 2.0/3.0) {
+      float z = 3.0 * subpixel_shift - 1.0;
+      r = mix(previous.b, previous.g, z);
+      g = mix(current.r,  previous.b, z);
+      b = mix(current.g,  current.r,  z);
+    } else if (subpixel_shift < 1.0) {
+      float z = 3.0 * subpixel_shift - 2.0;
+      r = mix(previous.g, previous.r, z);
+      g = mix(previous.b, previous.g, z);
+      b = mix(current.r,  previous.b, z);
+    }
+
+    vec3 pixel_coverages = vec3(r, g, b);
+
+    if(coverage_adjustment >= 0){
+      pixel_coverages = min(pixel_coverages * (1 + coverage_adjustment), 1);
+    }else{
+      pixel_coverages = max((1 - (1 - pixel_coverages) * (1 + -coverage_adjustment)), 0);
+    }
+
+    fragment_color = color * vec4(pixel_coverages, 1);
+    blend_weights  = vec4(color.a * pixel_coverages, color.a);
+}

glyph/shaders/font_vert.glsl

@@ -0,0 +1,45 @@
+#version 450 core
+#extension GL_ARB_texture_rectangle: enable
+
+
+layout(location=0) uniform vec2 half_viewport_size;
+
+//layout(location=0) in uvec2 ltrb_index;
+layout(location=0) in vec4  rect_ltrb;
+layout(location=1) in vec4  rect_tex_ltrb;
+layout(location=2) in vec4  rect_color;
+//layout(location=4) in uint  index;
+layout(location=3) in float rect_subpixel_shift;
+
+
+flat out vec2  tex_coords;
+flat out vec4  color;
+flat out float subpixel_shift;
+flat out uint   index_out;
+
+
+void main(){
+  uvec2[6] rect_vertices = {
+    {0, 1}, //left top
+    {0, 3}, //left buttom
+    {2, 1}, //right top
+    {0, 3}, //Left buttom
+    {2, 3}, //right bottom
+    {2, 1}, //right top
+  };
+  //Convert color to pre-multipled alpha
+
+  uvec2 indexx =  rect_vertices[gl_VertexID];
+
+  color = vec4(rect_color.rgb * rect_color.a, rect_color.a);
+
+  vec2 pos   = vec2(    rect_ltrb[indexx.x],     rect_ltrb[indexx.y]);
+  tex_coords = vec2(rect_tex_ltrb[indexx.x], rect_tex_ltrb[indexx.y]);
+  subpixel_shift = rect_subpixel_shift;
+  //index_out      = index;
+
+
+  vec2 axes_flip  = vec2(1, -1); // to flip y axis from bottom up
+  vec2 pos_in_ndc = (pos / half_viewport_size - 1.0) * axes_flip;
+  gl_Position = vec4(pos_in_ndc, 0, 1);
+}