From bf79653fa253d5c0f2e77c4c94aec445ffd2fbf9 Mon Sep 17 00:00:00 2001
From: Bernd Busse <bernd@busse-net.de>
Date: Thu, 24 Jun 2021 18:47:40 +0200
Subject: [PATCH] backend: gl_common: Copy texture by explict rendering to
 framebuffer

At least on nvidia, binding the textures from a glx pixmap to a
framebuffer results in `GL_FRAMEBUFFER_UNSUPPORTED`. Instead of using
binding the source texture to a framebuffer and using `glCopyTexImage2D()`
to copy into a new texture, explicitly render the source texture to the
new texture attached to a framebuffer.

Fixes black/invisible windows on nvidia with `frame-opacity != 1`.

see: #647

related: 2a60836a9bc30d92b4adb46d5f48684a5d2f1ecb
---
 src/backend/gl/gl_common.c | 82 ++++++++++++++++++++++++++++++++++----
 1 file changed, 74 insertions(+), 8 deletions(-)

diff --git a/src/backend/gl/gl_common.c b/src/backend/gl/gl_common.c
index 1a19b0e..e0a7848 100644
--- a/src/backend/gl/gl_common.c
+++ b/src/backend/gl/gl_common.c
@@ -1765,18 +1765,84 @@ static inline void gl_image_decouple(backend_t *base, struct backend_image *img)
 	new_tex->refcount = 1;
 	new_tex->user_data = gd->decouple_texture_user_data(base, inner->user_data);
 
+	glBindTexture(GL_TEXTURE_2D, new_tex->texture);
+	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, new_tex->width, new_tex->height, 0,
+	             GL_BGRA, GL_UNSIGNED_BYTE, NULL);
+	glBindTexture(GL_TEXTURE_2D, 0);
+
+	assert(gd->present_prog);
+	glUseProgram(gd->present_prog);
+	glBindTexture(GL_TEXTURE_2D, inner->texture);
+
 	GLuint fbo;
 	glGenFramebuffers(1, &fbo);
-	glBindFramebuffer(GL_READ_FRAMEBUFFER, fbo);
-	glFramebufferTexture2D(GL_READ_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D,
-	                       inner->texture, 0);
-	glReadBuffer(GL_COLOR_ATTACHMENT0);
-	glBindTexture(GL_TEXTURE_2D, new_tex->texture);
-	glCopyTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, 0, 0, new_tex->width, new_tex->height, 0);
-	glBindTexture(GL_TEXTURE_2D, 0);
-	glBindFramebuffer(GL_READ_FRAMEBUFFER, 0);
+	glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fbo);
+	glFramebufferTexture2D(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D,
+	                       new_tex->texture, 0);
+	glDrawBuffer(GL_COLOR_ATTACHMENT0);
+	gl_check_fb_complete(GL_DRAW_FRAMEBUFFER);
+
+	glClearColor(0, 0, 0, 0);
+	glClear(GL_COLOR_BUFFER_BIT);
+
+	// clang-format off
+	GLint coord[] = {
+		// top left
+		0, 0,                 // vertex coord
+		0, 0,                 // texture coord
+
+		// top right
+		new_tex->width, 0, // vertex coord
+		new_tex->width, 0, // texture coord
+
+		// bottom right
+		new_tex->width, new_tex->height,
+		new_tex->width, new_tex->height,
+
+		// bottom left
+		0, new_tex->height,
+		0, new_tex->height,
+	};
+	// clang-format on
+	GLuint indices[] = {0, 1, 2, 2, 3, 0};
+
+	GLuint vao;
+	glGenVertexArrays(1, &vao);
+	glBindVertexArray(vao);
+
+	GLuint bo[2];
+	glGenBuffers(2, bo);
+	glBindBuffer(GL_ARRAY_BUFFER, bo[0]);
+	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, bo[1]);
+	glBufferData(GL_ARRAY_BUFFER, (long)sizeof(*coord) * 16, coord, GL_STATIC_DRAW);
+	glBufferData(GL_ELEMENT_ARRAY_BUFFER, (long)sizeof(*indices) * 6, indices,
+	             GL_STATIC_DRAW);
+
+	glEnableVertexAttribArray(vert_coord_loc);
+	glEnableVertexAttribArray(vert_in_texcoord_loc);
+	glVertexAttribPointer(vert_coord_loc, 2, GL_INT, GL_FALSE, sizeof(GLint) * 4, NULL);
+	glVertexAttribPointer(vert_in_texcoord_loc, 2, GL_INT, GL_FALSE,
+	                      sizeof(GLint) * 4, (void *)(sizeof(GLint) * 2));
+
+	glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, NULL);
+
+	glDisableVertexAttribArray(vert_coord_loc);
+	glDisableVertexAttribArray(vert_in_texcoord_loc);
+	glBindVertexArray(0);
+	glDeleteVertexArrays(1, &vao);
+
+	glBindBuffer(GL_ARRAY_BUFFER, 0);
+	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
+	glDeleteBuffers(2, bo);
+
+	glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
 	glDeleteFramebuffers(1, &fbo);
 
+	glBindTexture(GL_TEXTURE_2D, 0);
+	glUseProgram(0);
+
+	gl_check_err();
+
 	img->inner = (struct backend_image_inner_base *)new_tex;
 	inner->refcount--;
 }