get imgui properly running in viewer

platform/imgui_backend/imgui_backend.go

@@ -299,7 +299,7 @@ func createFontTexture() uint32 {
 	// Store our identifier
 	io.Fonts().SetTextureID(imgui.TextureID(fontTexture))
 
-	// Restore singleton
+	// Restore state
 	gl.BindTexture(gl.TEXTURE_2D, uint32(lastTexture))
 	return fontTexture
 }

platform/window.go

@@ -82,11 +82,11 @@ func (w *Window) RenderTexture(texture *Texture, srcRect, dstRect math.Rect4i) {
 
 func (w *Window) advance() {
 	imgui_backend.NewFrame(w.displaySize())
+	w.sdlRenderer.Clear()
+
 	w.scene.Advance(w)
 
 	imgui.Render()
-
-	w.sdlWindow.GLMakeCurrent(w.sdlGlContext)
 	imgui_backend.Render(w.displaySize(), w.bufferSize(), imgui.RenderedDrawData())
 	w.sdlWindow.GLSwap()
 }

tools/viewer/main.go

@@ -5,6 +5,7 @@ import (
 	"log"
 	"os"
 
+	imgui "github.com/FooSoft/imgui-go"
 	"github.com/FooSoft/lazarus/formats/dat"
 	"github.com/FooSoft/lazarus/formats/dc6"
 	"github.com/FooSoft/lazarus/math"
@@ -62,6 +63,8 @@ func (s *scene) Init(window *platform.Window) error {
 }
 
 func (s *scene) Advance(window *platform.Window) error {
+	imgui.Text("Hello")
+
 	window.RenderTexture(
 		s.texture,
 		math.Rect4i{X: 0, Y: 0, W: 256, H: 256},