gl: implement readTexture (#9652)

This implementation is just a refactor of readPixels.

Author: poweifeng

filament/backend/src/opengl/OpenGLDriver.cpp

@@ -3985,10 +3985,8 @@ void OpenGLDriver::stopCapture(int) {
 // Read-back ops
 // ------------------------------------------------------------------------------------------------
 
-void OpenGLDriver::readPixels(Handle<HwRenderTarget> src,
-        uint32_t const x, uint32_t const y, uint32_t width, uint32_t height,
-        PixelBufferDescriptor&& p) {
-    DEBUG_MARKER()
+void OpenGLDriver::readPixelsFromBoundFramebuffer(uint32_t const x, uint32_t const y,
+        uint32_t width, uint32_t height, PixelBufferDescriptor&& p) {
     auto& gl = mContext;
 
     GLenum const glFormat = getFormat(p.format);
@@ -4021,8 +4019,6 @@ void OpenGLDriver::readPixels(Handle<HwRenderTarget> src,
      *                                  of the buffer.
      */
 
-    GLRenderTarget const* s = handle_cast<GLRenderTarget const*>(src);
-
     using PBD = PixelBufferDescriptor;
 
     // The PBO only needs to accommodate the area we're reading, with alignment.
@@ -4032,7 +4028,6 @@ void OpenGLDriver::readPixels(Handle<HwRenderTarget> src,
     if (UTILS_UNLIKELY(gl.isES2())) {
         void* buffer = malloc(pboSize);
         if (buffer) {
-            gl.bindFramebuffer(GL_FRAMEBUFFER, s->gl.fbo_read ? s->gl.fbo_read : s->gl.fbo);
             glReadPixels(GLint(x), GLint(y), GLint(width), GLint(height), glFormat, glType, buffer);
             CHECK_GL_ERROR()
 
@@ -4056,10 +4051,6 @@ void OpenGLDriver::readPixels(Handle<HwRenderTarget> src,
     }
 
 #ifndef FILAMENT_SILENCE_NOT_SUPPORTED_BY_ES2
-    // glReadPixel doesn't resolve automatically, but it does with the auto-resolve extension,
-    // which we're always emulating. So if we have a resolved fbo (fbo_read), use that instead.
-    gl.bindFramebuffer(GL_READ_FRAMEBUFFER, s->gl.fbo_read ? s->gl.fbo_read : s->gl.fbo);
-
     GLuint pbo;
     glGenBuffers(1, &pbo);
     gl.bindBuffer(GL_PIXEL_PACK_BUFFER, pbo);
@@ -4111,10 +4102,83 @@ void OpenGLDriver::readPixels(Handle<HwRenderTarget> src,
 #endif
 }
 
+void OpenGLDriver::readPixels(Handle<HwRenderTarget> src, uint32_t const x, uint32_t const y,
+        uint32_t width, uint32_t height, PixelBufferDescriptor&& p) {
+    DEBUG_MARKER()
+    auto& gl = mContext;
+
+    GLRenderTarget const* s = handle_cast<GLRenderTarget const*>(src);
+
+    if (UTILS_UNLIKELY(gl.isES2())) {
+        gl.bindFramebuffer(GL_FRAMEBUFFER, s->gl.fbo_read ? s->gl.fbo_read : s->gl.fbo);
+        readPixelsFromBoundFramebuffer(x, y, width, height, std::move(p));
+        return;
+    }
+
+#ifndef FILAMENT_SILENCE_NOT_SUPPORTED_BY_ES2
+    // glReadPixel doesn't resolve automatically, but it does with the auto-resolve extension,
+    // which we're always emulating. So if we have a resolved fbo (fbo_read), use that instead.
+    gl.bindFramebuffer(GL_READ_FRAMEBUFFER, s->gl.fbo_read ? s->gl.fbo_read : s->gl.fbo);
+    readPixelsFromBoundFramebuffer(x, y, width, height, std::move(p));
+#endif
+}
+
 void OpenGLDriver::readTexture(Handle<HwTexture> src, uint8_t level, uint16_t layer, uint32_t x,
         uint32_t y, uint32_t width, uint32_t height, PixelBufferDescriptor&& p) {
-    // TODO: implement readTexture
+    DEBUG_MARKER()
+    auto& gl = mContext;
+
+    // readTexture() requires GLES 3.0+ features such as GL_READ_FRAMEBUFFER and
+    // glFramebufferTextureLayer, so we wrap it in FILAMENT_SILENCE_NOT_SUPPORTED_BY_ES2.
+#ifndef FILAMENT_SILENCE_NOT_SUPPORTED_BY_ES2
+    if (UTILS_UNLIKELY(gl.isES2())) {
+        // This is not supported on ES2 (at least not in this driver)
+        scheduleDestroy(std::move(p));
+        return;
+    }
+
+    GLTexture const* s = handle_cast<GLTexture*>(src);
+    assert_invariant(s);
+    assert_invariant(s->target != SamplerType::SAMPLER_3D);
+
+    GLuint fbo = 0;
+    glGenFramebuffers(1, &fbo);
+    gl.bindFramebuffer(GL_READ_FRAMEBUFFER, fbo);
+
+    GLenum const attachment = GL_COLOR_ATTACHMENT0;
+
+    switch (s->target) {
+        case SamplerType::SAMPLER_2D:
+            if (any(s->usage & TextureUsage::SAMPLEABLE)) {
+                glFramebufferTexture2D(GL_READ_FRAMEBUFFER, attachment, GL_TEXTURE_2D, s->gl.id,
+                        level);
+            } else {
+                glFramebufferRenderbuffer(GL_READ_FRAMEBUFFER, attachment, GL_RENDERBUFFER,
+                        s->gl.id);
+            }
+            break;
+        case SamplerType::SAMPLER_CUBEMAP:
+            glFramebufferTexture2D(GL_READ_FRAMEBUFFER, attachment,
+                    GL_TEXTURE_CUBE_MAP_POSITIVE_X + layer, s->gl.id, level);
+            break;
+        case SamplerType::SAMPLER_2D_ARRAY:
+        case SamplerType::SAMPLER_CUBEMAP_ARRAY:
+            glFramebufferTextureLayer(GL_READ_FRAMEBUFFER, attachment, s->gl.id, level, layer);
+            break;
+        default:
+            // This should not happen (e.g. 3D textures are excluded)
+            break;
+    }
+
+    CHECK_GL_FRAMEBUFFER_STATUS(GL_READ_FRAMEBUFFER)
+
+    readPixelsFromBoundFramebuffer(x, y, width, height, std::move(p));
+
+    gl.unbindFramebuffer(GL_READ_FRAMEBUFFER);
+    glDeleteFramebuffers(1, &fbo);
+#else
     scheduleDestroy(std::move(p));
+#endif
 }
 
 void OpenGLDriver::readBufferSubData(BufferObjectHandle boh,

filament/backend/src/opengl/OpenGLDriver.h

@@ -363,6 +363,8 @@ class OpenGLDriver final : public OpenGLDriverBase {
             bool isDefaultFramebuffer) noexcept;
 
     // Common methods
+    void readPixelsFromBoundFramebuffer(uint32_t x, uint32_t y, uint32_t width, uint32_t height,
+            PixelBufferDescriptor&& p);
     void createTextureCommon(Handle<HwTexture> th, SamplerType target, uint8_t levels,
             TextureFormat format, uint8_t samples, uint32_t width, uint32_t height, uint32_t depth,
             TextureUsage usage, utils::ImmutableCString&& tag);

filament/backend/test/test_ReadTexture.cpp

@@ -51,7 +51,6 @@ class ReadTextureTest : public BackendTest {
 };
 
 TEST_F(ReadTextureTest, ReadTexture2D) {
-    SKIP_IF(Backend::OPENGL, "readTexture not implemented for OpenGL");
     SKIP_IF(Backend::METAL, "readTexture not implemented for Metal");
 
     DriverApi& api = getDriverApi();
@@ -147,7 +146,6 @@ TEST_F(ReadTextureTest, ReadTexture2D) {
 }
 
 TEST_F(ReadTextureTest, ReadTextureArray) {
-    SKIP_IF(Backend::OPENGL, "readTexture not implemented for OpenGL");
     SKIP_IF(Backend::METAL, "readTexture not implemented for Metal");
 
     DriverApi& api = getDriverApi();