[Sofa.GL] DrawToolGL: improve indices text rendering quality (#6093)

* auto-scale indices display based on camera distance

The indices text now maintains a constant screen-space size regardless of zoom level and scene dimensions, removing the need to manually adjust showIndicesScale per scene.

  - Compute per-vertex scale from the projection matrix and camera depth in GlText::textureDraw_Indices
  - Handle both perspective and orthographic projections
  - Add alpha blending for smoother text rendering
  - Update all callers to pass a dimensionless multiplier (default 1.0) instead of bbox-dependent world-space size

* improve indices text rendering quality

- Add drop shadow (black, 70% opacity, 1.5px offset) behind each label for readability against any background
- Disable depth test so indices always render on top of geometry
- Enable mipmaps on the ASCII texture atlas for cleaner downsampling

* set an option to render with depth test (true by default)

---------

Co-authored-by: Hugo <hugo.talbot@sofa-framework.org>

Author: fredroy

Sofa/GL/src/sofa/gl/glText.cpp

@@ -38,7 +38,7 @@ void GlText::initTexture()
     }
     if (s_asciiTexture == nullptr && s_asciiImage != nullptr)
     {
-        s_asciiTexture = new sofa::gl::Texture(s_asciiImage, false, true, false );
+        s_asciiTexture = new sofa::gl::Texture(s_asciiImage, false, true, true );
     }
 }
 
@@ -170,7 +170,7 @@ void GlText::textureDraw_Overlay(const char* text, const double scale)
 
 }
 
-void GlText::textureDraw_Indices(const type::vector<type::Vec3>& positions, const float& scale)
+void GlText::textureDraw_Indices(const type::vector<type::Vec3>& positions, const float& scale, bool enableDepthTest)
 {
     if (!s_asciiTexture)
     {
@@ -211,8 +211,17 @@ void GlText::textureDraw_Indices(const type::vector<type::Vec3>& positions, cons
     glEnable(GL_BLEND);
     glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
 
+    if(!enableDepthTest)
+        glDisable(GL_DEPTH_TEST);
+
+    glDisable(GL_LIGHTING);
+
     s_asciiTexture->bind();
 
+    // Save the caller-set color for the main text pass
+    GLfloat textColor[4];
+    glGetFloatv(GL_CURRENT_COLOR, textColor);
+
     for (std::size_t i = 0; i < positions.size(); i++)
     {
         std::ostringstream oss;
@@ -223,8 +232,6 @@ void GlText::textureDraw_Indices(const type::vector<type::Vec3>& positions, cons
         std::vector<Vec3f> vertices;
         std::vector<Vec2f> UVs;
 
-        glDisable(GL_LIGHTING);
-
         glPushMatrix();
 
         // Makes text always face the viewer by removing the scene rotation
@@ -248,11 +255,7 @@ void GlText::textureDraw_Indices(const type::vector<type::Vec3>& positions, cons
             autoScale = baseFontPixelHeight * scale * 2.0f / (p11 * viewportHeight);
         }
 
-        glLoadIdentity();
-        //translate a little bit to center the text on the position (instead of starting from a top-left position)
-        glTranslatef(temp[0] - (worldWidth*length*autoScale)*0.5f, temp[1] + worldHeight*autoScale*0.5f, temp[2]);
-        glScalef(autoScale, autoScale, autoScale);
-        glRotatef(180.0, 1, 0, 0);
+        // Build quads for this label
         for (std::size_t j = 0; j < length; j++)
         {
             Vec3f vertex_up_left = Vec3f(j*worldWidth, worldHeight, 0.0f);
@@ -281,6 +284,31 @@ void GlText::textureDraw_Indices(const type::vector<type::Vec3>& positions, cons
             UVs.push_back(uv_up_right);
         }
 
+        // Shadow offset: 1.5 pixels in view space
+        const float shadowOffset = 1.5f * autoScale / baseFontPixelHeight;
+
+        // Drop shadow pass (dark, offset down-right)
+        glColor4f(0.0f, 0.0f, 0.0f, textColor[3] * 0.7f);
+        glLoadIdentity();
+        glTranslatef(temp[0] - (worldWidth*length*autoScale)*0.5f + shadowOffset,
+                     temp[1] + worldHeight*autoScale*0.5f - shadowOffset,
+                     temp[2]);
+        glScalef(autoScale, autoScale, autoScale);
+        glRotatef(180.0, 1, 0, 0);
+        glBegin(GL_QUADS);
+        for (std::size_t j = 0; j < vertices.size(); j++)
+        {
+            glTexCoord2fv(UVs[j].data());
+            glVertex3fv(vertices[j].data());
+        }
+        glEnd();
+
+        // Main text pass
+        glColor4fv(textColor);
+        glLoadIdentity();
+        glTranslatef(temp[0] - (worldWidth*length*autoScale)*0.5f, temp[1] + worldHeight*autoScale*0.5f, temp[2]);
+        glScalef(autoScale, autoScale, autoScale);
+        glRotatef(180.0, 1, 0, 0);
         glBegin(GL_QUADS);
         for (std::size_t j = 0; j < vertices.size(); j++)
         {
@@ -295,9 +323,9 @@ void GlText::textureDraw_Indices(const type::vector<type::Vec3>& positions, cons
     s_asciiTexture->unbind();
     glDisable(GL_ALPHA_TEST);
     glDisable(GL_BLEND);
+    glEnable(GL_DEPTH_TEST);
     glPopAttrib();
 
-
     glEnable(GL_LIGHTING);
 }
 

Sofa/GL/src/sofa/gl/glText.h

@@ -75,7 +75,7 @@ class SOFA_GL_API GlText
     static void draw ( const T& text, const type::Vec3& position = type::Vec3(0.0,0.0,0.0), const double& scale = 1.0);
 
     static void textureDraw_Overlay(const char* text, const double scale = 1.0);
-    static void textureDraw_Indices(const type::vector<type::Vec3>& positions, const float& scale);
+    static void textureDraw_Indices(const type::vector<type::Vec3>& positions, const float& scale, bool enableDepthTest = true);
 
 private:
     static void initTexture();