No need to use a texture for the cursor; we can just use a fragment shader.

interface/resources/shaders/metavoxel_heightfield_cursor.frag

@@ -11,10 +11,22 @@
 //  See the accompanying file LICENSE or http://www.apache.org/licenses/LICENSE-2.0.html
 //
 
-// the cursor texture
-uniform sampler2D cursorMap;
+// the inner radius of the outline, squared
+const float SQUARED_OUTLINE_INNER_RADIUS = 0.81;
+
+// the outer radius of the outline, squared
+const float SQUARED_OUTLINE_OUTER_RADIUS = 1.0;
+
+// the inner radius of the inset, squared
+const float SQUARED_INSET_INNER_RADIUS = 0.855625;
+
+// the outer radius of the inset, squared
+const float SQUARED_INSET_OUTER_RADIUS = 0.950625;
 
 void main(void) {
-    // just multiply the color by the cursor texture
-    gl_FragColor = gl_Color * texture2D(cursorMap, gl_TexCoord[0].st);
+    // use the distance to compute the ring color, then multiply it by the varying color
+    float squaredDistance = dot(gl_TexCoord[0].st, gl_TexCoord[0].st);
+    float alpha = step(SQUARED_OUTLINE_INNER_RADIUS, squaredDistance) * step(squaredDistance, SQUARED_OUTLINE_OUTER_RADIUS);
+    float white = step(SQUARED_INSET_INNER_RADIUS, squaredDistance) * step(squaredDistance, SQUARED_INSET_OUTER_RADIUS);
+    gl_FragColor = gl_Color * vec4(white, white, white, alpha);
 }

interface/src/MetavoxelSystem.cpp

@@ -31,10 +31,6 @@ REGISTER_META_OBJECT(StaticModelRenderer)
 
 static int bufferPointVectorMetaTypeId = qRegisterMetaType<BufferPointVector>();
 
-MetavoxelSystem::MetavoxelSystem() :
-    _cursorTexture(QOpenGLTexture::Target2D) {
-}
-
 void MetavoxelSystem::init() {
     MetavoxelClientManager::init();
     DefaultMetavoxelRendererImplementation::init();
@@ -155,33 +151,6 @@ int HeightfieldCursorRenderVisitor::visit(MetavoxelInfo& info) {
 }
 
 void MetavoxelSystem::renderHeightfieldCursor(const glm::vec3& position, float radius) {
-    // create the cursor texture lazily
-    if (!_cursorTexture.isCreated()) {
-        const int CURSOR_TEXTURE_SIZE = 512;
-        QImage cursorImage(CURSOR_TEXTURE_SIZE, CURSOR_TEXTURE_SIZE, QImage::Format_ARGB32_Premultiplied);
-        cursorImage.fill(0x0);
-        {
-            QPainter painter(&cursorImage);
-            const int ELLIPSE_EDGE = 10;
-            const int OUTER_WIDTH = 10;
-            QPen outerPen;
-            outerPen.setWidth(OUTER_WIDTH);
-            painter.setPen(outerPen);
-            const int HALF_TEXTURE_SIZE = CURSOR_TEXTURE_SIZE / 2;
-            painter.drawEllipse(QPoint(HALF_TEXTURE_SIZE, HALF_TEXTURE_SIZE), HALF_TEXTURE_SIZE - ELLIPSE_EDGE,
-                HALF_TEXTURE_SIZE - ELLIPSE_EDGE);
-            QPen innerPen(Qt::white);
-            const int INNER_WIDTH = 6;
-            innerPen.setWidth(INNER_WIDTH);
-            painter.setPen(innerPen);
-            painter.drawEllipse(QPoint(HALF_TEXTURE_SIZE, HALF_TEXTURE_SIZE), HALF_TEXTURE_SIZE - ELLIPSE_EDGE,
-                HALF_TEXTURE_SIZE - ELLIPSE_EDGE);
-        }
-        _cursorTexture.setData(cursorImage, QOpenGLTexture::DontGenerateMipMaps);
-        _cursorTexture.setWrapMode(QOpenGLTexture::ClampToEdge);
-        _cursorTexture.setMinificationFilter(QOpenGLTexture::Linear);
-    }
-   
     glDepthFunc(GL_LEQUAL);
     glEnable(GL_CULL_FACE);
     glEnable(GL_POLYGON_OFFSET_FILL);
@@ -196,21 +165,16 @@ void MetavoxelSystem::renderHeightfieldCursor(const glm::vec3& position, float r
     
     glActiveTexture(GL_TEXTURE4);
     float scale = 1.0f / radius;
-    glm::vec4 sCoefficients(scale, 0.0f, 0.0f, 0.5f - scale * position.x);
-    glm::vec4 tCoefficients(0.0f, 0.0f, scale, 0.5f - scale * position.z);
+    glm::vec4 sCoefficients(scale, 0.0f, 0.0f, -scale * position.x);
+    glm::vec4 tCoefficients(0.0f, 0.0f, scale, -scale * position.z);
     glTexGenfv(GL_S, GL_EYE_PLANE, (const GLfloat*)&sCoefficients);
     glTexGenfv(GL_T, GL_EYE_PLANE, (const GLfloat*)&tCoefficients);
-    
-    _cursorTexture.bind(1);
     glActiveTexture(GL_TEXTURE0);
     
     glm::vec3 extents(radius, radius, radius);
     HeightfieldCursorRenderVisitor visitor(getLOD(), Box(position - extents, position + extents));
     guideToAugmented(visitor);
     
-    _cursorTexture.release(1);
-    glActiveTexture(GL_TEXTURE0);
-    
     DefaultMetavoxelRendererImplementation::getHeightfieldCursorProgram().release();
     
     glDisableClientState(GL_TEXTURE_COORD_ARRAY);

interface/src/MetavoxelSystem.h

@@ -14,7 +14,6 @@
 
 #include <QList>
 #include <QOpenGLBuffer>
-#include <QOpenGLTexture>
 #include <QReadWriteLock>
 #include <QVector>
 
@@ -32,8 +31,6 @@ class MetavoxelSystem : public MetavoxelClientManager {
 
 public:
 
-    MetavoxelSystem();
-
     virtual void init();
 
     virtual MetavoxelLOD getLOD();
@@ -64,8 +61,6 @@ private:
     MetavoxelLOD _lod;
     QReadWriteLock _lodLock;
     Frustum _frustum;
-    
-    QOpenGLTexture _cursorTexture;
 };
 
 /// Describes contents of a point in a point buffer.