shader modes, draw a jank cursor

shaders/cell.f.glsl

@@ -1,6 +1,7 @@
 #version 330 core
 
 in vec2 glyph_tex_coords;
+flat in uint mode;
 
 // The color for this cell. If this is a background pass this is the
 // background color. Otherwise, this is the foreground color.
@@ -9,14 +10,19 @@ flat in vec4 color;
 // Font texture
 uniform sampler2D text;
 
-// Background or foreground pass.
-uniform int background;
+// See fragment shader
+const uint MODE_BG = 1u;
+const uint MODE_FG = 2u;
 
 void main() {
-    if (background == 1) {
+    switch (mode) {
+    case MODE_BG:
         gl_FragColor = color;
-    } else {
+        break;
+
+    case MODE_FG:
         float a = texture(text, glyph_tex_coords).r;
         gl_FragColor = vec4(color.rgb, color.a*a);
+        break;
     }
 }

shaders/cell.v.glsl

@@ -1,5 +1,12 @@
 #version 330 core
 
+// These are the possible modes that "mode" can be set to. This is
+// used to multiplex multiple render modes into a single shader.
+//
+// NOTE: this must be kept in sync with the fragment shader
+const uint MODE_BG = 1u;
+const uint MODE_FG = 2u;
+
 // The grid coordinates (x, y) where x < columns and y < rows
 layout (location = 0) in vec2 grid_coord;
 
@@ -18,6 +25,12 @@ layout (location = 4) in vec4 fg_color_in;
 // The background color for this cell in RGBA (0 to 1.0)
 layout (location = 5) in vec4 bg_color_in;
 
+// The mode of this shader. The mode determines what fields are used,
+// what the output will be, etc. This shader is capable of executing in
+// multiple "modes" so that we can share some logic and so that we can draw
+// the entire terminal grid in a single GPU pass.
+layout (location = 6) in uint mode_in;
+
 // The background or foreground color for the fragment, depending on
 // whether this is a background or foreground pass.
 flat out vec4 color;
@@ -25,15 +38,37 @@ flat out vec4 color;
 // The x/y coordinate for the glyph representing the font.
 out vec2 glyph_tex_coords;
 
+// Pass the mode forward to the fragment shader.
+flat out uint mode;
+
 uniform sampler2D text;
 uniform vec2 cell_size;
 uniform mat4 projection;
 
-// non-zero if this is a background pass where we draw the background
-// of the cell. We do a background pass followed by a foreground pass.
-uniform int background;
+/********************************************************************
+ * Modes
+ *
+ *-------------------------------------------------------------------
+ * MODE_BG
+ *
+ * In MODE_BG, this shader renders only the background color for the
+ * cell. This is a simple mode where we generate a simple rectangle
+ * made up of 4 vertices and then it is filled. In this mode, the output
+ * "color" is the fill color for the bg.
+ *
+ *-------------------------------------------------------------------
+ * MODE_FG
+ *
+ * In MODE_FG, the shader renders the glyph onto this cell and utilizes
+ * the glyph texture "text". In this mode, the output "color" is the
+ * fg color to use for the glyph.
+ *
+ */
 
 void main() {
+    // We always forward our mode
+    mode = mode_in;
+
     // Top-left cell coordinates converted to world space
     // Example: (1,0) with a 30 wide cell is converted to (30,0)
     vec2 cell_pos = cell_size * grid_coord;
@@ -52,7 +87,8 @@ void main() {
     position.x = (gl_VertexID == 0 || gl_VertexID == 1) ? 1. : 0.;
     position.y = (gl_VertexID == 0 || gl_VertexID == 3) ? 0. : 1.;
 
-    if (background == 1) {
+    switch (mode_in) {
+    case MODE_BG:
         // Calculate the final position of our cell in world space.
         // We have to add our cell size since our vertices are offset
         // one cell up and to the left. (Do the math to verify yourself)
@@ -60,7 +96,9 @@ void main() {
 
         gl_Position = projection * vec4(cell_pos, 0.0, 1.0);
         color = bg_color_in / 255.0;
-    } else {
+        break;
+
+    case MODE_FG:
         // The glyph offset is upside down so we need to reverse it to
         // be based on the offset of our cell. This is equivalent to
         // "1 - value" to flip the value.
@@ -80,5 +118,6 @@ void main() {
 
         // Set our foreground color output
         color = fg_color_in / 255.;
+        break;
     }
 }

src/Grid.zig

@@ -41,16 +41,16 @@ const GPUCell = struct {
     grid_row: u16,
 
     /// vec2 glyph_pos
-    glyph_x: u32,
-    glyph_y: u32,
+    glyph_x: u32 = 0,
+    glyph_y: u32 = 0,
 
     /// vec2 glyph_size
-    glyph_width: u32,
-    glyph_height: u32,
+    glyph_width: u32 = 0,
+    glyph_height: u32 = 0,
 
     /// vec2 glyph_size
-    glyph_offset_x: i32,
-    glyph_offset_y: i32,
+    glyph_offset_x: i32 = 0,
+    glyph_offset_y: i32 = 0,
 
     /// vec4 fg_color_in
     fg_r: u8,
@@ -63,6 +63,9 @@ const GPUCell = struct {
     bg_g: u8,
     bg_b: u8,
     bg_a: u8,
+
+    /// uint mode
+    mode: u8,
 };
 
 pub fn init(alloc: Allocator) !Grid {
@@ -148,18 +151,22 @@ pub fn init(alloc: Allocator) !Grid {
     try vbobind.attributeAdvanced(4, 4, gl.c.GL_UNSIGNED_BYTE, false, @sizeOf(GPUCell), offset);
     offset += 4 * @sizeOf(u8);
     try vbobind.attributeAdvanced(5, 4, gl.c.GL_UNSIGNED_BYTE, false, @sizeOf(GPUCell), offset);
+    offset += 4 * @sizeOf(u8);
+    try vbobind.attributeIAdvanced(6, 1, gl.c.GL_UNSIGNED_BYTE, @sizeOf(GPUCell), offset);
     try vbobind.enableAttribArray(0);
     try vbobind.enableAttribArray(1);
     try vbobind.enableAttribArray(2);
     try vbobind.enableAttribArray(3);
     try vbobind.enableAttribArray(4);
     try vbobind.enableAttribArray(5);
+    try vbobind.enableAttribArray(6);
     try vbobind.attributeDivisor(0, 1);
     try vbobind.attributeDivisor(1, 1);
     try vbobind.attributeDivisor(2, 1);
     try vbobind.attributeDivisor(3, 1);
     try vbobind.attributeDivisor(4, 1);
     try vbobind.attributeDivisor(5, 1);
+    try vbobind.attributeDivisor(6, 1);
 
     // Build our texture
     const tex = try gl.Texture.create();
@@ -239,6 +246,7 @@ pub fn updateCells(self: *Grid, term: Terminal) !void {
         term.screen.items.len * term.cols,
     );
 
+    // Build each cell
     for (term.screen.items) |line, y| {
         for (line.items) |cell, x| {
             // It can be zero if the cell is empty
@@ -248,6 +256,7 @@ pub fn updateCells(self: *Grid, term: Terminal) !void {
             // TODO: if we add a glyph, I think we need to rerender the texture.
             const glyph = try self.font_atlas.addGlyph(self.alloc, cell.char);
 
+            // TODO: for background colors, add another cell with mode = 1
             self.cells.appendAssumeCapacity(.{
                 .grid_col = @intCast(u16, x),
                 .grid_row = @intCast(u16, y),
@@ -265,9 +274,25 @@ pub fn updateCells(self: *Grid, term: Terminal) !void {
                 .bg_g = 0xA5,
                 .bg_b = 0,
                 .bg_a = 0,
+                .mode = 2,
             });
         }
     }
+
+    // Draw the cursor
+    self.cells.appendAssumeCapacity(.{
+        .grid_col = @intCast(u16, term.cursor.x),
+        .grid_row = @intCast(u16, term.cursor.y),
+        .fg_r = 0,
+        .fg_g = 0,
+        .fg_b = 0,
+        .fg_a = 0,
+        .bg_r = 0xFF,
+        .bg_g = 0xFF,
+        .bg_b = 0xFF,
+        .bg_a = 255,
+        .mode = 1,
+    });
 }
 
 /// Set the screen size for rendering. This will update the projection
@@ -319,15 +344,6 @@ pub fn render(self: Grid) !void {
     var texbind = try self.texture.bind(.@"2D");
     defer texbind.unbind();
 
-    try self.program.setUniform("background", 1);
-    try gl.drawElementsInstanced(
-        gl.c.GL_TRIANGLES,
-        6,
-        gl.c.GL_UNSIGNED_BYTE,
-        self.cells.items.len,
-    );
-
-    try self.program.setUniform("background", 0);
     try gl.drawElementsInstanced(
         gl.c.GL_TRIANGLES,
         6,

src/Window.zig

@@ -92,7 +92,7 @@ pub fn create(alloc: Allocator) !*Window {
     // Create our terminal
     var term = Terminal.init(grid.size.columns, grid.size.rows);
     errdefer term.deinit(alloc);
-    try term.append(alloc, "hello!\r\nworld!");
+    try term.append(alloc, "> ");
 
     self.* = .{
         .alloc = alloc,

src/opengl/Buffer.zig

@@ -170,6 +170,23 @@ pub const Binding = struct {
         try errors.getError();
     }
 
+    pub inline fn attributeIAdvanced(
+        _: Binding,
+        idx: c.GLuint,
+        size: c.GLint,
+        typ: c.GLenum,
+        stride: c.GLsizei,
+        offset: usize,
+    ) !void {
+        const offsetPtr = if (offset > 0)
+            @intToPtr(*const anyopaque, offset)
+        else
+            null;
+
+        c.glVertexAttribIPointer(idx, size, typ, stride, offsetPtr);
+        try errors.getError();
+    }
+
     pub inline fn unbind(b: *Binding) void {
         c.glBindBuffer(@enumToInt(b.target), 0);
         b.* = undefined;