Port starfield to static shaders

shaders/star_frag.glsl

@@ -0,0 +1,8 @@
+#version 120
+uniform sampler2D starTex;
+varying vec4 color;
+
+void main(void)
+{
+    gl_FragColor = texture2D(starTex, gl_PointCoord) * color;
+}

shaders/star_vert.glsl

@@ -0,0 +1,10 @@
+#version 120
+attribute float pointSize;
+varying vec4 color;
+
+void main(void)
+{
+    gl_PointSize = pointSize;
+    color = gl_Color;
+    gl_Position = ftransform();
+}

src/celengine/render.cpp

@@ -320,16 +320,12 @@ PointStarVertexBuffer::~PointStarVertexBuffer()
 
 void PointStarVertexBuffer::startSprites()
 {
-    ShaderProperties shadprop;
-    shadprop.staticShader = true;
-    shadprop.texUsage = ShaderProperties::PointSprite   |
-                        ShaderProperties::NormalTexture;
-    CelestiaGLProgram* prog = renderer.getShaderManager().getShader(shadprop);
+    CelestiaGLProgram* prog = renderer.getShaderManager().getShader("star");
     if (prog == nullptr)
         return;
 
     prog->use();
-    prog->pointScale = 1.0f;
+    prog->samplerParam("starTex") = 0;
 
     unsigned int stride = sizeof(StarVertex);
     glEnableClientState(GL_VERTEX_ARRAY);