2 files changed, 53 insertions, 0 deletions

diff --git a/drivers/gles3/rasterizer_storage_gles3.cpp b/drivers/gles3/rasterizer_storage_gles3.cpp
index f91ed35331..a8380b5518 100644
--- a/drivers/gles3/rasterizer_storage_gles3.cpp
+++ b/drivers/gles3/rasterizer_storage_gles3.cpp
@@ -828,6 +828,58 @@ void RasterizerStorageGLES3::texture_set_data(RID p_texture, const Ref<Image> &p
 	//texture_set_flags(p_texture,texture->flags);
 }
 
+// Uploads pixel data to a sub-region of a texture, for the specified mipmap.
+// The texture pixels must have been allocated before, because most features seen in texture_set_data() make no sense in a partial update.
+// TODO If we want this to be usable without pre-filling pixels with a full image, we have to call glTexImage2D() with null data.
+void RasterizerStorageGLES3::texture_set_data_partial(RID p_texture, const Ref<Image> &p_image, int src_x, int src_y, int src_w, int src_h, int dst_x, int dst_y, int p_dst_mip, VS::CubeMapSide p_cube_side) {
+
+	Texture *texture = texture_owner.get(p_texture);
+
+	ERR_FAIL_COND(!texture);
+	ERR_FAIL_COND(!texture->active);
+	ERR_FAIL_COND(texture->render_target);
+	ERR_FAIL_COND(texture->format != p_image->get_format());
+	ERR_FAIL_COND(p_image.is_null());
+	ERR_FAIL_COND(src_w <= 0 || src_h <= 0);
+	ERR_FAIL_COND(src_x < 0 || src_y < 0 || src_x + src_w > p_image->get_width() || src_y + src_h > p_image->get_height());
+	ERR_FAIL_COND(dst_x < 0 || dst_y < 0 || dst_x + src_w > texture->alloc_width || dst_y + src_h > texture->alloc_height);
+	ERR_FAIL_COND(p_dst_mip < 0 || p_dst_mip >= texture->mipmaps);
+
+	GLenum type;
+	GLenum format;
+	GLenum internal_format;
+	bool compressed;
+	bool srgb;
+
+	// Because OpenGL wants data as a dense array, we have to extract the sub-image if the source rect isn't the full image
+	Ref<Image> p_sub_img = p_image;
+	if (src_x > 0 || src_y > 0 || src_w != p_image->get_width() || src_h != p_image->get_height()) {
+		p_sub_img = p_image->get_rect(Rect2(src_x, src_y, src_w, src_h));
+	}
+
+	Ref<Image> img = _get_gl_image_and_format(p_sub_img, p_sub_img->get_format(), texture->flags, format, internal_format, type, compressed, srgb);
+
+	GLenum blit_target = (texture->target == GL_TEXTURE_CUBE_MAP) ? _cube_side_enum[p_cube_side] : GL_TEXTURE_2D;
+
+	PoolVector<uint8_t>::Read read = img->get_data().read();
+
+	glActiveTexture(GL_TEXTURE0);
+	glBindTexture(texture->target, texture->tex_id);
+
+	int src_data_size = img->get_data().size();
+	int src_ofs = 0;
+
+	if (texture->compressed) {
+		glPixelStorei(GL_UNPACK_ALIGNMENT, 4);
+		glCompressedTexSubImage2D(blit_target, p_dst_mip, dst_x, dst_y, src_w, src_h, internal_format, src_data_size, &read[src_ofs]);
+
+	} else {
+		glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
+		// `format` has to match the internal_format used when the texture was created
+		glTexSubImage2D(blit_target, p_dst_mip, dst_x, dst_y, src_w, src_h, format, type, &read[src_ofs]);
+	}
+}
+
 Ref<Image> RasterizerStorageGLES3::texture_get_data(RID p_texture, VS::CubeMapSide p_cube_side) const {
 
 	Texture *texture = texture_owner.get(p_texture);
diff --git a/drivers/gles3/rasterizer_storage_gles3.h b/drivers/gles3/rasterizer_storage_gles3.h
index ef2b247266..d96b5a3ca6 100644
--- a/drivers/gles3/rasterizer_storage_gles3.h
+++ b/drivers/gles3/rasterizer_storage_gles3.h
@@ -340,6 +340,7 @@ public:
 	virtual RID texture_create();
 	virtual void texture_allocate(RID p_texture, int p_width, int p_height, Image::Format p_format, uint32_t p_flags = VS::TEXTURE_FLAGS_DEFAULT);
 	virtual void texture_set_data(RID p_texture, const Ref<Image> &p_image, VS::CubeMapSide p_cube_side = VS::CUBEMAP_LEFT);
+	virtual void texture_set_data_partial(RID p_texture, const Ref<Image> &p_image, int src_x, int src_y, int src_w, int src_h, int dst_x, int dst_y, int p_dst_mip, VS::CubeMapSide p_cube_side = VS::CUBEMAP_LEFT);
 	virtual Ref<Image> texture_get_data(RID p_texture, VS::CubeMapSide p_cube_side = VS::CUBEMAP_LEFT) const;
 	virtual void texture_set_flags(RID p_texture, uint32_t p_flags);
 	virtual uint32_t texture_get_flags(RID p_texture) const;