fix an assert() when using custom render targets

we now always mask out target bits that don't exist in the render
target before converting them to GLenums.

Fixes #2285

filament/backend/src/opengl/OpenGLDriver.cpp

@@ -912,6 +912,7 @@ void OpenGLDriver::createRenderTargetR(Handle<HwRenderTarget> rth,
      */
 
     rt->gl.samples = samples;
+    rt->targets = targets;
 
     if (any(targets & TargetBufferFlags::COLOR_ALL)) {
         GLenum bufs[4] = { GL_NONE };
@@ -1861,10 +1862,12 @@ void OpenGLDriver::beginRenderPass(Handle<HwRenderTarget> rth,
 
     mRenderPassTarget = rth;
     mRenderPassParams = params;
-    const TargetBufferFlags clearFlags = params.flags.clear;
-    TargetBufferFlags discardFlags = params.flags.discardStart;
 
     GLRenderTarget* rt = handle_cast<GLRenderTarget*>(rth);
+
+    const TargetBufferFlags clearFlags = params.flags.clear & rt->targets;
+    TargetBufferFlags discardFlags = params.flags.discardStart & rt->targets;
+
     gl.bindFramebuffer(GL_FRAMEBUFFER, rt->gl.fbo);
 
     // glInvalidateFramebuffer appeared on GLES 3.0 and GL4.3, for simplicity we just
@@ -1923,7 +1926,7 @@ void OpenGLDriver::endRenderPass(int) {
 
     GLRenderTarget const* const rt = handle_cast<GLRenderTarget*>(mRenderPassTarget);
 
-    const TargetBufferFlags discardFlags = mRenderPassParams.flags.discardEnd;
+    const TargetBufferFlags discardFlags = mRenderPassParams.flags.discardEnd & rt->targets;
     if (rt->gl.fbo_read) {
         resolvePass(ResolveAction::STORE, rt, discardFlags);
     }
@@ -1977,7 +1980,9 @@ void OpenGLDriver::resolvePass(ResolveAction action, GLRenderTarget const* rt,
 }
 
 GLsizei OpenGLDriver::getAttachments(std::array<GLenum, 6>& attachments,
-        GLRenderTarget const* rt, TargetBufferFlags buffers) const noexcept {
+        GLRenderTarget const* rt, TargetBufferFlags buffers) noexcept {
+    assert(buffers <= rt->targets);
+
     GLsizei attachmentCount = 0;
     // the default framebuffer uses different constants!!!
     const bool defaultFramebuffer = (rt->gl.fbo == 0);

filament/backend/src/opengl/OpenGLDriver.h

@@ -177,6 +177,7 @@ class OpenGLDriver final : public backend::DriverBase {
             mutable backend::TargetBufferFlags resolve = backend::TargetBufferFlags::NONE; // attachments in fbo_draw to resolve
             uint8_t samples : 4;
         } gl;
+        backend::TargetBufferFlags targets;
     };
 
     OpenGLDriver(OpenGLDriver const&) = delete;
@@ -337,8 +338,8 @@ class OpenGLDriver final : public backend::DriverBase {
         return mSamplerBindings;
     }
 
-    GLsizei getAttachments(std::array<GLenum, 6>& attachments,
-            GLRenderTarget const* rt, backend::TargetBufferFlags buffers) const noexcept;
+    static GLsizei getAttachments(std::array<GLenum, 6>& attachments,
+            GLRenderTarget const* rt, backend::TargetBufferFlags buffers) noexcept;
 
     backend::RasterState mRasterState;