add more model & shader examples

examples/shaders/eratosthenes/main.go

@@ -0,0 +1,42 @@
+package main
+
+import (
+	rl "github.com/gen2brain/raylib-go/raylib"
+)
+
+func main() {
+	screenWidth := int32(800)
+	screenHeight := int32(450)
+
+	rl.InitWindow(screenWidth, screenHeight, "raylib [shaders] example - Eratosthenes")
+
+	shader := rl.LoadShader("", "eratosthenes.fs")
+	target := rl.LoadRenderTexture(screenWidth, screenHeight)
+
+	rl.SetTargetFPS(60)
+
+	for !rl.WindowShouldClose() {
+
+		rl.BeginTextureMode(target)
+		rl.ClearBackground(rl.Black)
+		rl.DrawRectangle(0, 0, int32(rl.GetScreenWidth()), int32(rl.GetScreenHeight()), rl.Black)
+		rl.EndTextureMode()
+
+		rl.BeginDrawing()
+
+		rl.ClearBackground(rl.RayWhite)
+
+		rl.BeginShaderMode(shader)
+
+		rl.DrawTextureRec(target.Texture, rl.NewRectangle(0, 0, float32(target.Texture.Width), float32(target.Texture.Height)), rl.Vector2Zero(), rl.White)
+
+		rl.EndShaderMode()
+
+		rl.EndDrawing()
+	}
+
+	rl.UnloadShader(shader)
+	rl.UnloadRenderTexture(target)
+
+	rl.CloseWindow()
+}