Optimize rendering

This moves some logic that was previously being done per-character into
the vertex shader. At this time, we've traded CPU computation for
additional gl::Uniform2f calls. This is only a marginal improvement.
However, this patch positions the renderer well for instanced drawing,
and that will be a huge performance win.

1 files changed, 32 insertions, 3 deletions

diff --git a/res/text.v.glsl b/res/text.v.glsl
index 07a50376..c6543352 100644
--- a/res/text.v.glsl
+++ b/res/text.v.glsl
@@ -1,12 +1,41 @@
 #version 330 core
 layout (location = 0) in vec2 position;
-layout (location = 1) in vec2 uvMask;
+
 out vec2 TexCoords;
 
+// Terminal properties
+uniform vec2 termDim;
+uniform vec2 cellDim;
+uniform vec2 cellSep;
+
+// Cell properties
+uniform vec2 gridCoords;
+
+// glyph properties
+uniform vec2 glyphScale;
+uniform vec2 glyphOffset;
+
+// uv mapping
+uniform vec2 uvScale;
+uniform vec2 uvOffset;
+
+// Orthographic projection
 uniform mat4 projection;
 
 void main()
 {
-    gl_Position = projection * vec4(position.xy, 0.0, 1.0);
-    TexCoords = uvMask.xy;
+    // Position of cell from top-left
+    vec2 cellPosition = (cellDim + cellSep) * gridCoords;
+
+    // Invert Y since framebuffer origin is bottom-left
+    cellPosition.y = termDim.y - cellPosition.y - cellDim.y;
+
+    // Glyphs are offset within their cell; account for y-flip
+    vec2 cellOffset = vec2(glyphOffset.x, glyphOffset.y - glyphScale.y);
+
+    // position coordinates are normalized on [0, 1]
+    vec2 finalPosition = glyphScale * position + cellPosition + cellOffset;
+
+    gl_Position = projection * vec4(finalPosition.xy, 0.0, 1.0);
+    TexCoords = vec2(position.x, 1 - position.y) * uvScale + uvOffset;
 }