Renderer|Models: Use an alternative depth buffer for 3D psprites

It is unacceptable to clear the depth buffer for 3D psprites as that
would remove the depth information required for flare occlusion.

Now 3D psprites use their own, separate depth buffer.

Todo: Clean this up.

doomsday/client/src/render/sprite.cpp

@@ -39,9 +39,12 @@
 #include "resource/sprites.h"
 
 #include "render/vissprite.h"
-
 #include "render/sprite.h"
 
+#include <de/GLState>
+#include <de/GLTarget>
+#include <de/GLTexture>
+
 using namespace de;
 
 void Rend_RenderSprite(rendspriteparams_t const *params);
@@ -104,9 +107,15 @@ void Rend_Draw3DPlayerSprites()
     // Setup the modelview matrix.
     Rend_ModelViewMatrix(false /* don't apply view angle rotation */);
 
-    // Clear Z buffer. This will prevent the psprites from being clipped
-    // by nearby polygons.
-    glClear(GL_DEPTH_BUFFER_BIT);
+    bool zBufferHasBeenSetUp = false;
+
+    /// @todo Set up an easier API for switching depth buffer temporarily
+
+    GLTarget &target = GLState::current().target();
+    GLTexture *originalDepth = target.attachedTexture(GLTarget::DepthStencil);
+    DENG2_ASSERT(originalDepth != 0);
+
+    static GLTexture localDepth;
 
     rendmodelparams_t parm;
     for(int i = 0; i < DDMAXPSPRITES; ++i)
@@ -115,9 +124,27 @@ void Rend_Draw3DPlayerSprites()
 
         if(spr->type != VPSPR_MODEL) continue; // Not used.
 
+        if(!zBufferHasBeenSetUp)
+        {
+            // Resize the local depth buffer to match target size.
+            if(localDepth.size() != target.size())
+            {
+                localDepth.setDepthStencilContent(target.size());
+            }
+            target.replaceAttachment(GLTarget::DepthStencil, localDepth);
+            target.clear(GLTarget::DepthStencil);
+            zBufferHasBeenSetUp = true;
+        }
+
         setupModelParamsForVisPSprite(&parm, spr);
         Rend_RenderModel(&parm);
     }
+
+    // Restore the old depth/stencil buffer.
+    if(zBufferHasBeenSetUp)
+    {
+        target.replaceAttachment(GLTarget::DepthStencil, *originalDepth);
+    }
 }
 
 /**

doomsday/client/src/ui/clientwindow.cpp

@@ -819,6 +819,8 @@ void ClientWindow::drawGameContentToTexture(GLTexture &texture)
     DENG_ASSERT_IN_MAIN_THREAD();
     DENG_ASSERT_GL_CONTEXT_ACTIVE();
 
+    /// @todo Use GLFramebuffer
+
     GLTarget offscreen(texture, GLTarget::DepthStencil);
     GLState::push()
             .setTarget(offscreen)

doomsday/libgui/include/de/gui/gltarget.h

@@ -183,6 +183,14 @@ class LIBGUI_PUBLIC GLTarget : public Asset
      */
     GLTexture *attachedTexture(Flags const &attachment) const;
 
+    /**
+     * Replaces a currently attached texture with another.
+     *
+     * @param attachment  Which attachment.
+     * @param texture     New texture to use as the attachment.
+     */
+    void replaceAttachment(Flags const &attachment, GLTexture &texture);
+
     /**
      * Sets the subregion inside the render target where scissor and viewport
      * will be scaled into. Scissor and viewport can still be defined as if the

doomsday/libgui/src/gltarget.cpp

@@ -62,6 +62,18 @@ DENG2_OBSERVES(Asset, Deletion)
         return ColorBuffer; // should not be reached
     }
 
+    static GLenum flagsToGLAttachment(Flags const &flags)
+    {
+        DENG2_ASSERT(!flags.testFlag(ColorDepth));
+        DENG2_ASSERT(!flags.testFlag(ColorDepthStencil));
+
+        return flags == Color?   GL_COLOR_ATTACHMENT0  :
+               flags == Depth?   GL_DEPTH_ATTACHMENT   :
+               flags == Stencil? GL_STENCIL_ATTACHMENT :
+                                 GL_DEPTH_STENCIL_ATTACHMENT;
+    }
+
+
     GLuint fbo;
     GLuint renderBufs[MAX_ATTACHMENTS];
     GLTexture *bufTextures[MAX_ATTACHMENTS];
@@ -253,6 +265,18 @@ DENG2_OBSERVES(Asset, Deletion)
         allocRenderBuffers();
     }
 
+    void replace(GLenum attachment, GLTexture &newTexture)
+    {
+        DENG2_ASSERT(self.isReady());       // must already be inited
+        DENG2_ASSERT(bufTextures[attachmentToId(attachment)] != 0); // must have an attachment already
+
+        glBindFramebuffer(GL_FRAMEBUFFER, fbo);
+        attachTexture(newTexture, attachment);
+
+        // Restore previous target.
+        GLState::current().target().glBind();
+    }
+
     void validate()
     {
         if(isDefault())
@@ -462,6 +486,13 @@ GLTexture *GLTarget::attachedTexture(Flags const &attachment) const
     return d->bufferTexture(attachment);
 }
 
+void GLTarget::replaceAttachment(Flags const &attachment, GLTexture &texture)
+{
+    DENG2_ASSERT(!d->isDefault());
+
+    d->replace(d->flagsToGLAttachment(attachment), texture);
+}
+
 GLuint GLTarget::glName() const
 {
     return d->fbo;