GPUState: Move Scissor and Viewport state to framebuffer

This way it is way clearer what each viewport state is. There is
no more save and reset. The scissor test is also saved per
framebuffer.

The only rule to remember is that the viewport state (size and
origin) is reset for both the viewport and scissor when a texture
is attached or detached from an attachment slot.

source/blender/gpu/opengl/gl_framebuffer.cc

@@ -27,6 +27,7 @@
 
 #include "gl_backend.hh"
 #include "gl_framebuffer.hh"
+#include "gl_state.hh"
 #include "gl_texture.hh"
 
 namespace blender::gpu {
@@ -47,6 +48,7 @@ GLFrameBuffer::GLFrameBuffer(
     : FrameBuffer(name)
 {
   context_ = ctx;
+  state_manager_ = static_cast<GLStateManager *>(ctx->state_manager);
   immutable_ = true;
   fbo_id_ = fbo;
   gl_attachments_[0] = target;
@@ -56,6 +58,11 @@ GLFrameBuffer::GLFrameBuffer(
   height_ = h;
   srgb_ = false;
 
+  viewport_[0] = scissor_[0] = 0;
+  viewport_[1] = scissor_[1] = 0;
+  viewport_[2] = scissor_[2] = w;
+  viewport_[3] = scissor_[3] = h;
+
 #ifndef __APPLE__
   if (fbo_id_ && (G.debug & G_DEBUG_GPU) && (GLEW_VERSION_4_3 || GLEW_KHR_debug)) {
     char sh_name[32];
@@ -82,6 +89,7 @@ GLFrameBuffer::~GLFrameBuffer()
 void GLFrameBuffer::init(void)
 {
   context_ = static_cast<GLContext *>(GPU_context_active_get());
+  state_manager_ = static_cast<GLStateManager *>(context_->state_manager);
   glGenFramebuffers(1, &fbo_id_);
 
 #ifndef __APPLE__
@@ -227,6 +235,25 @@ void GLFrameBuffer::update_attachments(void)
   }
 }
 
+void GLFrameBuffer::apply_state(void)
+{
+  if (dirty_state_ == false) {
+    return;
+  }
+
+  glViewport(UNPACK4(viewport_));
+  glScissor(UNPACK4(scissor_));
+
+  if (scissor_test_) {
+    glEnable(GL_SCISSOR_TEST);
+  }
+  else {
+    glDisable(GL_SCISSOR_TEST);
+  }
+
+  dirty_state_ = false;
+}
+
 /** \} */
 
 /* -------------------------------------------------------------------- */
@@ -235,18 +262,16 @@ void GLFrameBuffer::update_attachments(void)
 
 void GLFrameBuffer::bind(bool enabled_srgb)
 {
-  GPUContext *ctx = GPU_context_active_get();
-  BLI_assert(ctx);
-
-  if (context_ != NULL && context_ != ctx) {
-    BLI_assert(!"Trying to use the same framebuffer in multiple context");
-  }
-
   if (!immutable_ && fbo_id_ == 0) {
     this->init();
   }
 
-  if (ctx->active_fb != this) {
+  if (context_ != GPU_context_active_get()) {
+    BLI_assert(!"Trying to use the same framebuffer in multiple context");
+    return;
+  }
+
+  if (context_->active_fb != this) {
     glBindFramebuffer(GL_FRAMEBUFFER, fbo_id_);
     /* Internal framebuffers have only one color output and needs to be set everytime. */
     if (immutable_ && fbo_id_ == 0) {
@@ -256,10 +281,14 @@ void GLFrameBuffer::bind(bool enabled_srgb)
 
   if (dirty_attachments_) {
     this->update_attachments();
+    this->viewport_reset();
+    this->scissor_reset();
   }
 
-  if (ctx->active_fb != this) {
-    ctx->active_fb = this;
+  if (context_->active_fb != this) {
+    context_->active_fb = this;
+    state_manager_->active_fb = this;
+    dirty_state_ = true;
 
     if (enabled_srgb) {
       glEnable(GL_FRAMEBUFFER_SRGB);
@@ -270,8 +299,6 @@ void GLFrameBuffer::bind(bool enabled_srgb)
 
     GPU_shader_set_framebuffer_srgb_target(enabled_srgb && srgb_);
   }
-
-  GPU_viewport(0, 0, width_, height_);
 }
 
 /** \} */
@@ -285,6 +312,9 @@ void GLFrameBuffer::clear(eGPUFrameBufferBits buffers,
                           float clear_depth,
                           uint clear_stencil)
 {
+  BLI_assert(GPU_context_active_get() == context_);
+  BLI_assert(context_->active_fb == this);
+
   /* Save and restore the state. */
   eGPUWriteMask write_mask = GPU_write_mask_get();
   uint stencil_mask = GPU_stencil_mask_get();
@@ -320,6 +350,9 @@ void GLFrameBuffer::clear(eGPUFrameBufferBits buffers,
 
 void GLFrameBuffer::clear_multi(const float (*clear_cols)[4])
 {
+  BLI_assert(GPU_context_active_get() == context_);
+  BLI_assert(context_->active_fb == this);
+
   /* Save and restore the state. */
   eGPUWriteMask write_mask = GPU_write_mask_get();
   GPU_color_mask(true, true, true, true);
@@ -401,7 +434,7 @@ void GLFrameBuffer::blit_to(
     glDrawBuffer(dst->gl_attachments_[dst_slot]);
   }
 
-  GPU_context_active_get()->state_manager->apply_state();
+  context_->state_manager->apply_state();
 
   int w = src->width_;
   int h = src->height_;