OpenGL: add WebGL support for ReadPixels.

google · Jun 13, 2022 · 7294e7f · 7294e7f
1 parent 3476429
commit 7294e7f
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Showing 3 changed files with 21 additions and 3 deletions.
diff --git a/RELEASE_NOTES.md b/RELEASE_NOTES.md
@@ -11,6 +11,7 @@ A new header is inserted each time a *tag* is created.
 - engine: Documentation improvements regarding SkinningBuffer and fix an off-by-one assert when setting a SkinningBuffer.
 - picking is now exposed to JavaScript
 - gltf_viewer: Exercise picking functionality.
+- OpenGL: add WebGL support for ReadPixels
 
 ## v1.23.2
 

diff --git a/filament/backend/src/opengl/OpenGLDriver.cpp b/filament/backend/src/opengl/OpenGLDriver.cpp
@@ -1687,7 +1687,7 @@ void OpenGLDriver::updateBuffer(GLBufferObject* buffer, BufferDescriptor const&
         // If MapBufferRange is supported, then attempt to use that instead of BufferSubData, which
         // can be quite inefficient on some platforms. Note that WebGL does not support
         // MapBufferRange, but we still allow STREAM semantics for the web platform.
-        if (HAS_MAPBUFFERS) {
+        if constexpr (HAS_MAPBUFFERS) {
             uint32_t offset = buffer->base + buffer->size;
             offset = (offset + (alignment - 1u)) & ~(alignment - 1u);
 
@@ -2622,7 +2622,15 @@ void OpenGLDriver::readPixels(Handle<HwRenderTarget> src,
         PixelBufferDescriptor& p = *pUserBuffer;
         auto& gl = mContext;
         gl.bindBuffer(GL_PIXEL_PACK_BUFFER, pbo);
-        void* vaddr = glMapBufferRange(GL_PIXEL_PACK_BUFFER, 0,  p.size, GL_MAP_READ_BIT);
+        void* vaddr = nullptr;
+        std::unique_ptr<uint8_t> clientBuffer;
+#if defined(__EMSCRIPTEN__)
+        clientBuffer.reset(new uint8_t(p.size));
+        glGetBufferSubData(GL_PIXEL_PACK_BUFFER, 0, p.size, clientBuffer.get());
+        vaddr = clientBuffer.get();
+#else
+        vaddr = glMapBufferRange(GL_PIXEL_PACK_BUFFER, 0,  p.size, GL_MAP_READ_BIT);
+#endif
         if (vaddr) {
             // now we need to flip the buffer vertically to match our API
             size_t stride = p.stride ? p.stride : width;
@@ -2637,7 +2645,9 @@ void OpenGLDriver::readPixels(Handle<HwRenderTarget> src,
                 head += bpr;
                 tail -= bpr;
             }
-            glUnmapBuffer(GL_PIXEL_PACK_BUFFER);
+            if (HAS_MAPBUFFERS) {
+                glUnmapBuffer(GL_PIXEL_PACK_BUFFER);
+            }
         }
         gl.bindBuffer(GL_PIXEL_PACK_BUFFER, 0);
         glDeleteBuffers(1, &pbo);

diff --git a/filament/backend/src/opengl/gl_headers.h b/filament/backend/src/opengl/gl_headers.h
@@ -115,6 +115,13 @@
 
 #endif
 
+// This is an odd duck function that exists in WebGL 2.0 but not in OpenGL ES.
+#if defined(__EMSCRIPTEN__)
+extern "C" {
+void glGetBufferSubData(GLenum target, GLintptr offset, GLsizeiptr size, void *data);
+}
+#endif
+
 #if (!defined(GL_ES_VERSION_2_0) && !defined(GL_VERSION_4_1))
 #error "Minimum header version must be OpenGL ES 2.0 or OpenGL 4.1"
 #endif