Underline support (#193)

* added Tab Stops support

* added support for Screen Mode (DECSCNM) -- reverse colors

* bug fix: cursor rendition in Origin Mode

* bug fix: SGR parameters handling

* Save/Restore Cursor updates. Partial charset implementation.

* added Underline support

* fixed underline position

* underline position measured in MinY

gui/gui.go

@@ -19,10 +19,10 @@ import (
 	"github.com/kbinani/screenshot"
 	"github.com/liamg/aminal/buffer"
 	"github.com/liamg/aminal/config"
+	"github.com/liamg/aminal/platform"
 	"github.com/liamg/aminal/terminal"
 	"github.com/liamg/aminal/version"
 	"go.uber.org/zap"
-	"github.com/liamg/aminal/platform"
 )
 
 type GUI struct {
@@ -529,6 +529,35 @@ func (gui *GUI) redraw() {
 			}
 		}
 
+	}
+	// underlines
+	for y := 0; y < lineCount; y++ {
+
+		if y < len(lines) {
+
+			span := 0
+			colour := [3]float32{0, 0, 0}
+			cells := lines[y].Cells()
+
+			var x int
+
+			for x = 0; x < colCount && x < len(cells); x++ {
+				cell := cells[x]
+				if span > 0 && (!cell.Attr().Underline || colour != cell.Fg()) {
+					gui.renderer.DrawUnderline(span, uint(x-span), uint(y), colour)
+					span = 0
+				}
+
+				colour = cell.Fg()
+				if cell.Attr().Underline {
+					span++
+				}
+			}
+			if span > 0 {
+				gui.renderer.DrawUnderline(span, uint(x-span), uint(y), colour)
+			}
+		}
+
 	}
 	gui.renderOverlay()
 }

gui/renderer.go

@@ -46,7 +46,7 @@ func (r *OpenGLRenderer) CellHeight() float32 {
 	return r.cellHeight
 }
 
-func (r *OpenGLRenderer) newRectangle(x float32, y float32, colourAttr uint32) *rectangle {
+func (r *OpenGLRenderer) newRectangleEx(x float32, y float32, width float32, height float32, colourAttr uint32) *rectangle {
 
 	rect := &rectangle{}
 
@@ -55,8 +55,8 @@ func (r *OpenGLRenderer) newRectangle(x float32, y float32, colourAttr uint32) *
 
 	x = (x - halfAreaWidth) / halfAreaWidth
 	y = -(y - (halfAreaHeight)) / halfAreaHeight
-	w := r.cellWidth / halfAreaWidth
+	w := width / halfAreaWidth
-	h := (r.cellHeight) / halfAreaHeight
+	h := height / halfAreaHeight
 
 	rect.points = [18]float32{
 		x, y, 0,
@@ -91,6 +91,10 @@ func (r *OpenGLRenderer) newRectangle(x float32, y float32, colourAttr uint32) *
 	return rect
 }
 
+func (r *OpenGLRenderer) newRectangle(x float32, y float32, colourAttr uint32) *rectangle {
+	return r.newRectangleEx(x, y, r.cellWidth, r.cellHeight, colourAttr)
+}
+
 func (rect *rectangle) Draw() {
 	gl.UseProgram(rect.prog)
 	gl.BindVertexArray(rect.vao)
@@ -228,6 +232,24 @@ func (r *OpenGLRenderer) DrawCellBg(cell buffer.Cell, col uint, row uint, cursor
 
 }
 
+// DrawUnderline draws a line under 'span' characters starting at (col, row)
+func (r *OpenGLRenderer) DrawUnderline(span int, col uint, row uint, colour [3]float32) {
+	//calculate coordinates
+	x := float32(float32(col) * r.cellWidth)
+	y := (float32(row+1))*r.cellHeight + r.fontMap.DefaultFont().MinY()*0.25
+
+	thickness := r.cellHeight / 16
+	if thickness < 1 {
+		thickness = 1
+	}
+	rect := r.newRectangleEx(x, y, r.cellWidth*float32(span), thickness, r.colourAttr)
+
+	rect.setColour(colour)
+	rect.Draw()
+
+	rect.Free()
+}
+
 func (r *OpenGLRenderer) DrawCellText(text string, col uint, row uint, alpha float32, colour [3]float32, bold bool) {
 
 	var f *glfont.Font