// SPDX-License-Identifier: MIT
/*
 * Compton - a compositor for X11
 *
 * Based on `xcompmgr` - Copyright (c) 2003, Keith Packard
 *
 * Copyright (c) 2011-2013, Christopher Jeffrey
 * See LICENSE-mit for more information.
 *
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <xcb/render.h>
#include <xcb/xcb.h>

#include "backend/gl/gl_common.h"
#include "backend/gl/glx.h"
#include "common.h"
#include "compiler.h"
#include "config.h"
#include "kernel.h"
#include "log.h"
#include "region.h"
#include "string_utils.h"
#include "uthash_extra.h"
#include "utils.h"
#include "win.h"

#include "opengl.h"

#ifndef GL_TEXTURE_RECTANGLE
#define GL_TEXTURE_RECTANGLE 0x84F5
#endif

static inline XVisualInfo *get_visualinfo_from_visual(session_t *ps, xcb_visualid_t visual) {
	XVisualInfo vreq = {.visualid = visual};
	int nitems = 0;

	return XGetVisualInfo(ps->dpy, VisualIDMask, &vreq, &nitems);
}

/**
 * Initialize OpenGL.
 */
bool glx_init(session_t *ps, bool need_render) {
	bool success = false;
	XVisualInfo *pvis = NULL;

	// Check for GLX extension
	if (!ps->glx_exists) {
		log_error("No GLX extension.");
		goto glx_init_end;
	}

	// Get XVisualInfo
	pvis = get_visualinfo_from_visual(ps, ps->vis);
	if (!pvis) {
		log_error("Failed to acquire XVisualInfo for current visual.");
		goto glx_init_end;
	}

	// Ensure the visual is double-buffered
	if (need_render) {
		int value = 0;
		if (Success != glXGetConfig(ps->dpy, pvis, GLX_USE_GL, &value) || !value) {
			log_error("Root visual is not a GL visual.");
			goto glx_init_end;
		}

		if (Success != glXGetConfig(ps->dpy, pvis, GLX_DOUBLEBUFFER, &value) || !value) {
			log_error("Root visual is not a double buffered GL visual.");
			goto glx_init_end;
		}
	}

	// Ensure GLX_EXT_texture_from_pixmap exists
	if (need_render && !glxext.has_GLX_EXT_texture_from_pixmap)
		goto glx_init_end;

	// Initialize GLX data structure
	if (!ps->psglx) {
		static const glx_session_t CGLX_SESSION_DEF = CGLX_SESSION_INIT;
		ps->psglx = cmalloc(glx_session_t);
		memcpy(ps->psglx, &CGLX_SESSION_DEF, sizeof(glx_session_t));

		// +1 for the zero terminator
		ps->psglx->blur_passes = ccalloc(ps->o.blur_kernel_count, glx_blur_pass_t);

		for (int i = 0; i < ps->o.blur_kernel_count; ++i) {
			glx_blur_pass_t *ppass = &ps->psglx->blur_passes[i];
			ppass->unifm_factor_center = -1;
			ppass->unifm_offset_x = -1;
			ppass->unifm_offset_y = -1;
		}
	}

	glx_session_t *psglx = ps->psglx;

	if (!psglx->context) {
		// Get GLX context
#ifndef DEBUG_GLX_DEBUG_CONTEXT
		psglx->context = glXCreateContext(ps->dpy, pvis, None, GL_TRUE);
#else
		{
			GLXFBConfig fbconfig = get_fbconfig_from_visualinfo(ps, pvis);
			if (!fbconfig) {
				log_error("Failed to get GLXFBConfig for root visual "
				          "%#lx.",
				          pvis->visualid);
				goto glx_init_end;
			}

			f_glXCreateContextAttribsARB p_glXCreateContextAttribsARB =
			    (f_glXCreateContextAttribsARB)glXGetProcAddress(
			        (const GLubyte *)"glXCreateContextAttribsARB");
			if (!p_glXCreateContextAttribsARB) {
				log_error("Failed to get glXCreateContextAttribsARB().");
				goto glx_init_end;
			}

			static const int attrib_list[] = {
			    GLX_CONTEXT_FLAGS_ARB, GLX_CONTEXT_DEBUG_BIT_ARB, None};
			psglx->context = p_glXCreateContextAttribsARB(
			    ps->dpy, fbconfig, NULL, GL_TRUE, attrib_list);
		}
#endif

		if (!psglx->context) {
			log_error("Failed to get GLX context.");
			goto glx_init_end;
		}

		// Attach GLX context
		if (!glXMakeCurrent(ps->dpy, get_tgt_window(ps), psglx->context)) {
			log_error("Failed to attach GLX context.");
			goto glx_init_end;
		}

#ifdef DEBUG_GLX_DEBUG_CONTEXT
		{
			f_DebugMessageCallback p_DebugMessageCallback =
			    (f_DebugMessageCallback)glXGetProcAddress(
			        (const GLubyte *)"glDebugMessageCallback");
			if (!p_DebugMessageCallback) {
				log_error("Failed to get glDebugMessageCallback(0.");
				goto glx_init_end;
			}
			p_DebugMessageCallback(glx_debug_msg_callback, ps);
		}
#endif
	}

	// Ensure we have a stencil buffer. X Fixes does not guarantee rectangles
	// in regions don't overlap, so we must use stencil buffer to make sure
	// we don't paint a region for more than one time, I think?
	if (need_render && !ps->o.glx_no_stencil) {
		GLint val = 0;
		glGetIntegerv(GL_STENCIL_BITS, &val);
		if (!val) {
			log_error("Target window doesn't have stencil buffer.");
			goto glx_init_end;
		}
	}

	// Check GL_ARB_texture_non_power_of_two, requires a GLX context and
	// must precede FBConfig fetching
	if (need_render)
		psglx->has_texture_non_power_of_two =
		    gl_has_extension("GL_ARB_texture_non_power_of_two");

	// Render preparations
	if (need_render) {
		glx_on_root_change(ps);

		glDisable(GL_DEPTH_TEST);
		glDepthMask(GL_FALSE);
		glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
		glDisable(GL_BLEND);

		if (!ps->o.glx_no_stencil) {
			// Initialize stencil buffer
			glClear(GL_STENCIL_BUFFER_BIT);
			glDisable(GL_STENCIL_TEST);
			glStencilMask(0x1);
			glStencilFunc(GL_EQUAL, 0x1, 0x1);
		}

		// Clear screen
		glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
		// glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
		// glXSwapBuffers(ps->dpy, get_tgt_window(ps));
	}

	success = true;

glx_init_end:
	XFree(pvis);

	if (!success)
		glx_destroy(ps);

	return success;
}

static void glx_free_prog_main(glx_prog_main_t *pprogram) {
	if (!pprogram)
		return;
	if (pprogram->prog) {
		glDeleteProgram(pprogram->prog);
		pprogram->prog = 0;
	}
	pprogram->unifm_opacity = -1;
	pprogram->unifm_invert_color = -1;
	pprogram->unifm_tex = -1;
}

/**
 * Destroy GLX related resources.
 */
void glx_destroy(session_t *ps) {
	if (!ps->psglx)
		return;

	// Free all GLX resources of windows
	win_stack_foreach_managed(w, &ps->window_stack) {
		free_win_res_glx(ps, w);
	}

	// Free GLSL shaders/programs
	for (int i = 0; i < ps->o.blur_kernel_count; ++i) {
		glx_blur_pass_t *ppass = &ps->psglx->blur_passes[i];
		if (ppass->frag_shader)
			glDeleteShader(ppass->frag_shader);
		if (ppass->prog)
			glDeleteProgram(ppass->prog);
	}
	free(ps->psglx->blur_passes);

	glx_free_prog_main(&ps->glx_prog_win);

	gl_check_err();

	// Destroy GLX context
	if (ps->psglx->context) {
		glXDestroyContext(ps->dpy, ps->psglx->context);
		ps->psglx->context = NULL;
	}

	free(ps->psglx);
	ps->psglx = NULL;
}

/**
 * Callback to run on root window size change.
 */
void glx_on_root_change(session_t *ps) {
	glViewport(0, 0, ps->root_width, ps->root_height);

	// Initialize matrix, copied from dcompmgr
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glOrtho(0, ps->root_width, 0, ps->root_height, -1000.0, 1000.0);
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
}

/**
 * Initialize GLX blur filter.
 */
bool glx_init_blur(session_t *ps) {
	assert(ps->o.blur_kernel_count > 0);
	assert(ps->o.blur_kerns);
	assert(ps->o.blur_kerns[0]);

	// Allocate PBO if more than one blur kernel is present
	if (ps->o.blur_kernel_count > 1) {
		// Try to generate a framebuffer
		GLuint fbo = 0;
		glGenFramebuffers(1, &fbo);
		if (!fbo) {
			log_error("Failed to generate Framebuffer. Cannot do multi-pass "
			          "blur with GLX"
			          " backend.");
			return false;
		}
		glDeleteFramebuffers(1, &fbo);
	}

	{
		char *lc_numeric_old = strdup(setlocale(LC_NUMERIC, NULL));
		// Enforce LC_NUMERIC locale "C" here to make sure decimal point is sane
		// Thanks to hiciu for reporting.
		setlocale(LC_NUMERIC, "C");

		static const char *FRAG_SHADER_BLUR_PREFIX =
		    "#version 110\n"
		    "%s"
		    "uniform float offset_x;\n"
		    "uniform float offset_y;\n"
		    "uniform float factor_center;\n"
		    "uniform %s tex_scr;\n"
		    "\n"
		    "void main() {\n"
		    "  vec4 sum = vec4(0.0, 0.0, 0.0, 0.0);\n";
		static const char *FRAG_SHADER_BLUR_ADD =
		    "  sum += float(%.7g) * %s(tex_scr, vec2(gl_TexCoord[0].x + offset_x "
		    "* float(%d), gl_TexCoord[0].y + offset_y * float(%d)));\n";
		static const char *FRAG_SHADER_BLUR_SUFFIX =
		    "  sum += %s(tex_scr, vec2(gl_TexCoord[0].x, gl_TexCoord[0].y)) * "
		    "factor_center;\n"
		    "  gl_FragColor = sum / (factor_center + float(%.7g));\n"
		    "}\n";

		const bool use_texture_rect = !ps->psglx->has_texture_non_power_of_two;
		const char *sampler_type = (use_texture_rect ? "sampler2DRect" : "sampler2D");
		const char *texture_func = (use_texture_rect ? "texture2DRect" : "texture2D");
		const char *shader_add = FRAG_SHADER_BLUR_ADD;
		char *extension = NULL;
		if (use_texture_rect) {
			mstrextend(&extension, "#extension GL_ARB_texture_rectangle : "
			                       "require\n");
		}
		if (!extension) {
			extension = strdup("");
		}

		for (int i = 0; i < ps->o.blur_kernel_count; ++i) {
			auto kern = ps->o.blur_kerns[i];
			glx_blur_pass_t *ppass = &ps->psglx->blur_passes[i];

			// Build shader
			int width = kern->w, height = kern->h;
			int nele = width * height - 1;
			assert(nele >= 0);
			auto len =
			    strlen(FRAG_SHADER_BLUR_PREFIX) + strlen(sampler_type) +
			    strlen(extension) +
			    (strlen(shader_add) + strlen(texture_func) + 42) * (uint)nele +
			    strlen(FRAG_SHADER_BLUR_SUFFIX) + strlen(texture_func) + 12 + 1;
			char *shader_str = ccalloc(len, char);
			char *pc = shader_str;
			sprintf(pc, FRAG_SHADER_BLUR_PREFIX, extension, sampler_type);
			pc += strlen(pc);
			assert(strlen(shader_str) < len);

			double sum = 0.0;
			for (int j = 0; j < height; ++j) {
				for (int k = 0; k < width; ++k) {
					if (height / 2 == j && width / 2 == k)
						continue;
					double val = kern->data[j * width + k];
					if (val == 0) {
						continue;
					}
					sum += val;
					sprintf(pc, shader_add, val, texture_func,
					        k - width / 2, j - height / 2);
					pc += strlen(pc);
					assert(strlen(shader_str) < len);
				}
			}

			sprintf(pc, FRAG_SHADER_BLUR_SUFFIX, texture_func, sum);
			assert(strlen(shader_str) < len);
			ppass->frag_shader = gl_create_shader(GL_FRAGMENT_SHADER, shader_str);
			free(shader_str);

			if (!ppass->frag_shader) {
				log_error("Failed to create fragment shader %d.", i);
				free(extension);
				free(lc_numeric_old);
				return false;
			}

			// Build program
			ppass->prog = gl_create_program(&ppass->frag_shader, 1);
			if (!ppass->prog) {
				log_error("Failed to create GLSL program.");
				free(extension);
				free(lc_numeric_old);
				return false;
			}

			// Get uniform addresses
#define P_GET_UNIFM_LOC(name, target)                                                    \
	{                                                                                \
		ppass->target = glGetUniformLocation(ppass->prog, name);                 \
		if (ppass->target < 0) {                                                 \
			log_error("Failed to get location of %d-th uniform '" name       \
			          "'. Might be troublesome.",                            \
			          i);                                                    \
		}                                                                        \
	}

			P_GET_UNIFM_LOC("factor_center", unifm_factor_center);
			P_GET_UNIFM_LOC("offset_x", unifm_offset_x);
			P_GET_UNIFM_LOC("offset_y", unifm_offset_y);

#undef P_GET_UNIFM_LOC
		}
		free(extension);

		// Restore LC_NUMERIC
		setlocale(LC_NUMERIC, lc_numeric_old);
		free(lc_numeric_old);
	}

	gl_check_err();

	return true;
}

/**
 * Load a GLSL main program from shader strings.
 */
bool glx_load_prog_main(const char *vshader_str, const char *fshader_str,
                        glx_prog_main_t *pprogram) {
	assert(pprogram);

	// Build program
	pprogram->prog = gl_create_program_from_str(vshader_str, fshader_str);
	if (!pprogram->prog) {
		log_error("Failed to create GLSL program.");
		return false;
	}

	// Get uniform addresses
#define P_GET_UNIFM_LOC(name, target)                                                    \
	{                                                                                \
		pprogram->target = glGetUniformLocation(pprogram->prog, name);           \
		if (pprogram->target < 0) {                                              \
			log_error("Failed to get location of uniform '" name             \
			          "'. Might be troublesome.");                           \
		}                                                                        \
	}
	P_GET_UNIFM_LOC("opacity", unifm_opacity);
	P_GET_UNIFM_LOC("invert_color", unifm_invert_color);
	P_GET_UNIFM_LOC("tex", unifm_tex);
	P_GET_UNIFM_LOC("time", unifm_time);
#undef P_GET_UNIFM_LOC

	gl_check_err();

	return true;
}

/**
 * Bind a X pixmap to an OpenGL texture.
 */
bool glx_bind_pixmap(session_t *ps, glx_texture_t **pptex, xcb_pixmap_t pixmap, int width,
                     int height, bool repeat, const struct glx_fbconfig_info *fbcfg) {
	if (ps->o.backend != BKEND_GLX && ps->o.backend != BKEND_XR_GLX_HYBRID)
		return true;

	if (!pixmap) {
		log_error("Binding to an empty pixmap %#010x. This can't work.", pixmap);
		return false;
	}

	assert(fbcfg);
	glx_texture_t *ptex = *pptex;
	bool need_release = true;

	// Release pixmap if parameters are inconsistent
	if (ptex && ptex->texture && ptex->pixmap != pixmap) {
		glx_release_pixmap(ps, ptex);
	}

	// Allocate structure
	if (!ptex) {
		static const glx_texture_t GLX_TEX_DEF = {
		    .texture = 0,
		    .glpixmap = 0,
		    .pixmap = 0,
		    .target = 0,
		    .width = 0,
		    .height = 0,
		    .y_inverted = false,
		};

		ptex = cmalloc(glx_texture_t);
		memcpy(ptex, &GLX_TEX_DEF, sizeof(glx_texture_t));
		*pptex = ptex;
	}

	// Create GLX pixmap
	int depth = 0;
	if (!ptex->glpixmap) {
		need_release = false;

		// Retrieve pixmap parameters, if they aren't provided
		if (!width || !height) {
			auto r = xcb_get_geometry_reply(
			    ps->c, xcb_get_geometry(ps->c, pixmap), NULL);
			if (!r) {
				log_error("Failed to query info of pixmap %#010x.", pixmap);
				return false;
			}
			if (r->depth > OPENGL_MAX_DEPTH) {
				log_error("Requested depth %d higher than %d.", depth,
				          OPENGL_MAX_DEPTH);
				return false;
			}
			depth = r->depth;
			width = r->width;
			height = r->height;
			free(r);
		}

		// Determine texture target, copied from compiz
		// The assumption we made here is the target never changes based on any
		// pixmap-specific parameters, and this may change in the future
		GLenum tex_tgt = 0;
		if (GLX_TEXTURE_2D_BIT_EXT & fbcfg->texture_tgts &&
		    ps->psglx->has_texture_non_power_of_two)
			tex_tgt = GLX_TEXTURE_2D_EXT;
		else if (GLX_TEXTURE_RECTANGLE_BIT_EXT & fbcfg->texture_tgts)
			tex_tgt = GLX_TEXTURE_RECTANGLE_EXT;
		else if (!(GLX_TEXTURE_2D_BIT_EXT & fbcfg->texture_tgts))
			tex_tgt = GLX_TEXTURE_RECTANGLE_EXT;
		else
			tex_tgt = GLX_TEXTURE_2D_EXT;

		log_debug("depth %d, tgt %#x, rgba %d", depth, tex_tgt,
		          (GLX_TEXTURE_FORMAT_RGBA_EXT == fbcfg->texture_fmt));

		GLint attrs[] = {
		    GLX_TEXTURE_FORMAT_EXT,
		    fbcfg->texture_fmt,
		    GLX_TEXTURE_TARGET_EXT,
		    (GLint)tex_tgt,
		    0,
		};

		ptex->glpixmap = glXCreatePixmap(ps->dpy, fbcfg->cfg, pixmap, attrs);
		ptex->pixmap = pixmap;
		ptex->target =
		    (GLX_TEXTURE_2D_EXT == tex_tgt ? GL_TEXTURE_2D : GL_TEXTURE_RECTANGLE);
		ptex->width = width;
		ptex->height = height;
		ptex->y_inverted = fbcfg->y_inverted;
	}
	if (!ptex->glpixmap) {
		log_error("Failed to allocate GLX pixmap.");
		return false;
	}

	glEnable(ptex->target);

	// Create texture
	if (!ptex->texture) {
		need_release = false;

		GLuint texture = 0;
		glGenTextures(1, &texture);
		glBindTexture(ptex->target, texture);

		glTexParameteri(ptex->target, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
		glTexParameteri(ptex->target, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
		if (repeat) {
			glTexParameteri(ptex->target, GL_TEXTURE_WRAP_S, GL_REPEAT);
			glTexParameteri(ptex->target, GL_TEXTURE_WRAP_T, GL_REPEAT);
		} else {
			glTexParameteri(ptex->target, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
			glTexParameteri(ptex->target, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
		}

		glBindTexture(ptex->target, 0);

		ptex->texture = texture;
	}
	if (!ptex->texture) {
		log_error("Failed to allocate texture.");
		return false;
	}

	glBindTexture(ptex->target, ptex->texture);

	// The specification requires rebinding whenever the content changes...
	// We can't follow this, too slow.
	if (need_release)
		glXReleaseTexImageEXT(ps->dpy, ptex->glpixmap, GLX_FRONT_LEFT_EXT);

	glXBindTexImageEXT(ps->dpy, ptex->glpixmap, GLX_FRONT_LEFT_EXT, NULL);

	// Cleanup
	glBindTexture(ptex->target, 0);
	glDisable(ptex->target);

	gl_check_err();

	return true;
}

/**
 * @brief Release binding of a texture.
 */
void glx_release_pixmap(session_t *ps, glx_texture_t *ptex) {
	// Release binding
	if (ptex->glpixmap && ptex->texture) {
		glBindTexture(ptex->target, ptex->texture);
		glXReleaseTexImageEXT(ps->dpy, ptex->glpixmap, GLX_FRONT_LEFT_EXT);
		glBindTexture(ptex->target, 0);
	}

	// Free GLX Pixmap
	if (ptex->glpixmap) {
		glXDestroyPixmap(ps->dpy, ptex->glpixmap);
		ptex->glpixmap = 0;
	}

	gl_check_err();
}

/**
 * Set clipping region on the target window.
 */
void glx_set_clip(session_t *ps, const region_t *reg) {
	// Quit if we aren't using stencils
	if (ps->o.glx_no_stencil)
		return;

	glDisable(GL_STENCIL_TEST);
	glDisable(GL_SCISSOR_TEST);

	if (!reg)
		return;

	int nrects;
	const rect_t *rects = pixman_region32_rectangles((region_t *)reg, &nrects);

	if (nrects == 1) {
		glEnable(GL_SCISSOR_TEST);
		glScissor(rects[0].x1, ps->root_height - rects[0].y2,
		          rects[0].x2 - rects[0].x1, rects[0].y2 - rects[0].y1);
	}

	gl_check_err();
}

#define P_PAINTREG_START(var)                                                            \
	region_t reg_new;                                                                \
	int nrects;                                                                      \
	const rect_t *rects;                                                             \
	assert(width >= 0 && height >= 0);                                               \
	pixman_region32_init_rect(&reg_new, dx, dy, (uint)width, (uint)height);          \
	pixman_region32_intersect(&reg_new, &reg_new, (region_t *)reg_tgt);              \
	rects = pixman_region32_rectangles(&reg_new, &nrects);                           \
	glBegin(GL_QUADS);                                                               \
                                                                                         \
	for (int ri = 0; ri < nrects; ++ri) {                                            \
		rect_t var = rects[ri];

#define P_PAINTREG_END()                                                                 \
	}                                                                                \
	glEnd();                                                                         \
                                                                                         \
	pixman_region32_fini(&reg_new);

static inline GLuint glx_gen_texture(GLenum tex_tgt, int width, int height) {
	GLuint tex = 0;
	glGenTextures(1, &tex);
	if (!tex)
		return 0;
	glEnable(tex_tgt);
	glBindTexture(tex_tgt, tex);
	glTexParameteri(tex_tgt, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
	glTexParameteri(tex_tgt, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
	glTexParameteri(tex_tgt, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
	glTexParameteri(tex_tgt, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
	glTexImage2D(tex_tgt, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);
	glBindTexture(tex_tgt, 0);

	return tex;
}

static inline void glx_copy_region_to_tex(session_t *ps, GLenum tex_tgt, int basex,
                                          int basey, int dx, int dy, int width, int height) {
	if (width > 0 && height > 0)
		glCopyTexSubImage2D(tex_tgt, 0, dx - basex, dy - basey, dx,
		                    ps->root_height - dy - height, width, height);
}

/**
 * Blur contents in a particular region.
 *
 * XXX seems to be way to complex for what it does
 */
bool glx_blur_dst(session_t *ps, int dx, int dy, int width, int height, float z,
                  GLfloat factor_center, const region_t *reg_tgt, glx_blur_cache_t *pbc) {
	assert(ps->psglx->blur_passes[0].prog);
	const bool more_passes = ps->o.blur_kernel_count > 1;
	const bool have_scissors = glIsEnabled(GL_SCISSOR_TEST);
	const bool have_stencil = glIsEnabled(GL_STENCIL_TEST);
	bool ret = false;

	// Calculate copy region size
	glx_blur_cache_t ibc = {.width = 0, .height = 0};
	if (!pbc)
		pbc = &ibc;

	int mdx = dx, mdy = dy, mwidth = width, mheight = height;
	// log_trace("%d, %d, %d, %d", mdx, mdy, mwidth, mheight);

	/*
	if (ps->o.resize_damage > 0) {
	  int inc_x = 0, inc_y = 0;
	  for (int i = 0; i < MAX_BLUR_PASS; ++i) {
	    XFixed *kern = ps->o.blur_kerns[i];
	    if (!kern) break;
	    inc_x += XFIXED_TO_DOUBLE(kern[0]) / 2;
	    inc_y += XFIXED_TO_DOUBLE(kern[1]) / 2;
	  }
	  inc_x = min2(ps->o.resize_damage, inc_x);
	  inc_y = min2(ps->o.resize_damage, inc_y);

	  mdx = max2(dx - inc_x, 0);
	  mdy = max2(dy - inc_y, 0);
	  int mdx2 = min2(dx + width + inc_x, ps->root_width),
	      mdy2 = min2(dy + height + inc_y, ps->root_height);
	  mwidth = mdx2 - mdx;
	  mheight = mdy2 - mdy;
	}
	*/

	GLenum tex_tgt = GL_TEXTURE_RECTANGLE;
	if (ps->psglx->has_texture_non_power_of_two)
		tex_tgt = GL_TEXTURE_2D;

	// Free textures if size inconsistency discovered
	if (mwidth != pbc->width || mheight != pbc->height)
		free_glx_bc_resize(ps, pbc);

	// Generate FBO and textures if needed
	if (!pbc->textures[0])
		pbc->textures[0] = glx_gen_texture(tex_tgt, mwidth, mheight);
	GLuint tex_scr = pbc->textures[0];
	if (more_passes && !pbc->textures[1])
		pbc->textures[1] = glx_gen_texture(tex_tgt, mwidth, mheight);
	pbc->width = mwidth;
	pbc->height = mheight;
	GLuint tex_scr2 = pbc->textures[1];
	if (more_passes && !pbc->fbo)
		glGenFramebuffers(1, &pbc->fbo);
	const GLuint fbo = pbc->fbo;

	if (!tex_scr || (more_passes && !tex_scr2)) {
		log_error("Failed to allocate texture.");
		goto glx_blur_dst_end;
	}
	if (more_passes && !fbo) {
		log_error("Failed to allocate framebuffer.");
		goto glx_blur_dst_end;
	}

	// Read destination pixels into a texture
	glEnable(tex_tgt);
	glBindTexture(tex_tgt, tex_scr);
	glx_copy_region_to_tex(ps, tex_tgt, mdx, mdy, mdx, mdy, mwidth, mheight);
	/*
	if (tex_scr2) {
	  glBindTexture(tex_tgt, tex_scr2);
	  glx_copy_region_to_tex(ps, tex_tgt, mdx, mdy, mdx, mdy, mwidth, dx - mdx);
	  glx_copy_region_to_tex(ps, tex_tgt, mdx, mdy, mdx, dy + height,
	      mwidth, mdy + mheight - dy - height);
	  glx_copy_region_to_tex(ps, tex_tgt, mdx, mdy, mdx, dy, dx - mdx, height);
	  glx_copy_region_to_tex(ps, tex_tgt, mdx, mdy, dx + width, dy,
	      mdx + mwidth - dx - width, height);
	} */

	// Texture scaling factor
	GLfloat texfac_x = 1.0f, texfac_y = 1.0f;
	if (tex_tgt == GL_TEXTURE_2D) {
		texfac_x /= (GLfloat)mwidth;
		texfac_y /= (GLfloat)mheight;
	}

	// Paint it back
	if (more_passes) {
		glDisable(GL_STENCIL_TEST);
		glDisable(GL_SCISSOR_TEST);
	}

	bool last_pass = false;
	for (int i = 0; i < ps->o.blur_kernel_count; ++i) {
		last_pass = (i == ps->o.blur_kernel_count - 1);
		const glx_blur_pass_t *ppass = &ps->psglx->blur_passes[i];
		assert(ppass->prog);

		assert(tex_scr);
		glBindTexture(tex_tgt, tex_scr);

		if (!last_pass) {
			glBindFramebuffer(GL_FRAMEBUFFER, fbo);
			glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
			                       GL_TEXTURE_2D, tex_scr2, 0);
			glDrawBuffer(GL_COLOR_ATTACHMENT0);
			if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) {
				log_error("Framebuffer attachment failed.");
				goto glx_blur_dst_end;
			}
		} else {
			glBindFramebuffer(GL_FRAMEBUFFER, 0);
			glDrawBuffer(GL_BACK);
			if (have_scissors)
				glEnable(GL_SCISSOR_TEST);
			if (have_stencil)
				glEnable(GL_STENCIL_TEST);
		}

		// Color negation for testing...
		// glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);
		// glTexEnvf(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_REPLACE);
		// glTexEnvf(GL_TEXTURE_ENV, GL_OPERAND0_RGB, GL_ONE_MINUS_SRC_COLOR);

		glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
		glUseProgram(ppass->prog);
		if (ppass->unifm_offset_x >= 0)
			glUniform1f(ppass->unifm_offset_x, texfac_x);
		if (ppass->unifm_offset_y >= 0)
			glUniform1f(ppass->unifm_offset_y, texfac_y);
		if (ppass->unifm_factor_center >= 0)
			glUniform1f(ppass->unifm_factor_center, factor_center);

		P_PAINTREG_START(crect) {
			auto rx = (GLfloat)(crect.x1 - mdx) * texfac_x;
			auto ry = (GLfloat)(mheight - (crect.y1 - mdy)) * texfac_y;
			auto rxe = rx + (GLfloat)(crect.x2 - crect.x1) * texfac_x;
			auto rye = ry - (GLfloat)(crect.y2 - crect.y1) * texfac_y;
			auto rdx = (GLfloat)(crect.x1 - mdx);
			auto rdy = (GLfloat)(mheight - crect.y1 + mdy);
			if (last_pass) {
				rdx = (GLfloat)crect.x1;
				rdy = (GLfloat)(ps->root_height - crect.y1);
			}
			auto rdxe = rdx + (GLfloat)(crect.x2 - crect.x1);
			auto rdye = rdy - (GLfloat)(crect.y2 - crect.y1);

			// log_trace("%f, %f, %f, %f -> %f, %f, %f, %f", rx, ry,
			// rxe, rye, rdx,
			//          rdy, rdxe, rdye);

			glTexCoord2f(rx, ry);
			glVertex3f(rdx, rdy, z);

			glTexCoord2f(rxe, ry);
			glVertex3f(rdxe, rdy, z);

			glTexCoord2f(rxe, rye);
			glVertex3f(rdxe, rdye, z);

			glTexCoord2f(rx, rye);
			glVertex3f(rdx, rdye, z);
		}
		P_PAINTREG_END();

		glUseProgram(0);

		// Swap tex_scr and tex_scr2
		{
			GLuint tmp = tex_scr2;
			tex_scr2 = tex_scr;
			tex_scr = tmp;
		}
	}

	ret = true;

glx_blur_dst_end:
	glBindFramebuffer(GL_FRAMEBUFFER, 0);
	glBindTexture(tex_tgt, 0);
	glDisable(tex_tgt);
	if (have_scissors)
		glEnable(GL_SCISSOR_TEST);
	if (have_stencil)
		glEnable(GL_STENCIL_TEST);

	if (&ibc == pbc) {
		free_glx_bc(ps, pbc);
	}

	gl_check_err();

	return ret;
}

bool glx_dim_dst(session_t *ps, int dx, int dy, int width, int height, int z,
                 GLfloat factor, const region_t *reg_tgt) {
	// It's possible to dim in glx_render(), but it would be over-complicated
	// considering all those mess in color negation and modulation
	glEnable(GL_BLEND);
	glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
	glColor4f(0.0f, 0.0f, 0.0f, factor);

	P_PAINTREG_START(crect) {
		// XXX what does all of these variables mean?
		GLint rdx = crect.x1;
		GLint rdy = ps->root_height - crect.y1;
		GLint rdxe = rdx + (crect.x2 - crect.x1);
		GLint rdye = rdy - (crect.y2 - crect.y1);

		glVertex3i(rdx, rdy, z);
		glVertex3i(rdxe, rdy, z);
		glVertex3i(rdxe, rdye, z);
		glVertex3i(rdx, rdye, z);
	}
	P_PAINTREG_END();

	glColor4f(0.0f, 0.0f, 0.0f, 0.0f);
	glDisable(GL_BLEND);

	gl_check_err();

	return true;
}

/**
 * @brief Render a region with texture data.
 */
bool glx_render(session_t *ps, const glx_texture_t *ptex, int x, int y, int dx, int dy,
                int width, int height, int z, double opacity, bool argb, bool neg,
                const region_t *reg_tgt, const glx_prog_main_t *pprogram) {
	if (!ptex || !ptex->texture) {
		log_error("Missing texture.");
		return false;
	}

	const bool has_prog = pprogram && pprogram->prog;
	bool dual_texture = false;

	// It's required by legacy versions of OpenGL to enable texture target
	// before specifying environment. Thanks to madsy for telling me.
	glEnable(ptex->target);

	// Enable blending if needed
	if (opacity < 1.0 || argb) {

		glEnable(GL_BLEND);

		// Needed for handling opacity of ARGB texture
		glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);

		// This is all weird, but X Render is using premultiplied ARGB format, and
		// we need to use those things to correct it. Thanks to derhass for help.
		glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
		glColor4d(opacity, opacity, opacity, opacity);
	}

	if (!has_prog) {
		// The default, fixed-function path
		// Color negation
		if (neg) {
			// Simple color negation
			if (!glIsEnabled(GL_BLEND)) {
				glEnable(GL_COLOR_LOGIC_OP);
				glLogicOp(GL_COPY_INVERTED);
			}
			// ARGB texture color negation
			else if (argb) {
				dual_texture = true;

				// Use two texture stages because the calculation is too
				// complicated, thanks to madsy for providing code Texture
				// stage 0
				glActiveTexture(GL_TEXTURE0);

				// Negation for premultiplied color: color = A - C
				glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);
				glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_SUBTRACT);
				glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB, GL_TEXTURE);
				glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_RGB, GL_SRC_ALPHA);
				glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_RGB, GL_TEXTURE);
				glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB, GL_SRC_COLOR);

				// Pass texture alpha through
				glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_ALPHA, GL_REPLACE);
				glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_ALPHA, GL_TEXTURE);
				glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_ALPHA, GL_SRC_ALPHA);

				// Texture stage 1
				glActiveTexture(GL_TEXTURE1);
				glEnable(ptex->target);
				glBindTexture(ptex->target, ptex->texture);

				glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);

				// Modulation with constant factor
				glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_MODULATE);
				glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB, GL_PREVIOUS);
				glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_RGB, GL_SRC_COLOR);
				glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_RGB, GL_PRIMARY_COLOR);
				glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB, GL_SRC_ALPHA);

				// Modulation with constant factor
				glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_ALPHA, GL_MODULATE);
				glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_ALPHA, GL_PREVIOUS);
				glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_ALPHA, GL_SRC_ALPHA);
				glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_ALPHA, GL_PRIMARY_COLOR);
				glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_ALPHA, GL_SRC_ALPHA);

				glActiveTexture(GL_TEXTURE0);
			}
			// RGB blend color negation
			else {
				glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);

				// Modulation with constant factor
				glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_MODULATE);
				glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB, GL_TEXTURE);
				glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_RGB,
				          GL_ONE_MINUS_SRC_COLOR);
				glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_RGB, GL_PRIMARY_COLOR);
				glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB, GL_SRC_COLOR);

				// Modulation with constant factor
				glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_ALPHA, GL_MODULATE);
				glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_ALPHA, GL_TEXTURE);
				glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_ALPHA, GL_SRC_ALPHA);
				glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_ALPHA, GL_PRIMARY_COLOR);
				glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_ALPHA, GL_SRC_ALPHA);
			}
		}
	} else {
		// Programmable path
		assert(pprogram->prog);
		glUseProgram(pprogram->prog);
		struct timespec ts;
		clock_gettime(CLOCK_MONOTONIC, &ts);
		if (pprogram->unifm_opacity >= 0)
			glUniform1f(pprogram->unifm_opacity, (float)opacity);
		if (pprogram->unifm_invert_color >= 0)
			glUniform1i(pprogram->unifm_invert_color, neg);
		if (pprogram->unifm_tex >= 0)
			glUniform1i(pprogram->unifm_tex, 0);
		if (pprogram->unifm_time >= 0)
			glUniform1f(pprogram->unifm_time, (float)ts.tv_sec * 1000.0f + (float)ts.tv_nsec / 1.0e6f);
	}

	// log_trace("Draw: %d, %d, %d, %d -> %d, %d (%d, %d) z %d", x, y, width, height,
	//          dx, dy, ptex->width, ptex->height, z);

	// Bind texture
	glBindTexture(ptex->target, ptex->texture);
	if (dual_texture) {
		glActiveTexture(GL_TEXTURE1);
		glBindTexture(ptex->target, ptex->texture);
		glActiveTexture(GL_TEXTURE0);
	}

	// Painting
	{
		P_PAINTREG_START(crect) {
			// XXX explain these variables
			auto rx = (GLfloat)(crect.x1 - dx + x);
			auto ry = (GLfloat)(crect.y1 - dy + y);
			auto rxe = rx + (GLfloat)(crect.x2 - crect.x1);
			auto rye = ry + (GLfloat)(crect.y2 - crect.y1);
			// Rectangle textures have [0-w] [0-h] while 2D texture has [0-1]
			// [0-1] Thanks to amonakov for pointing out!
			if (GL_TEXTURE_2D == ptex->target) {
				rx = rx / (GLfloat)ptex->width;
				ry = ry / (GLfloat)ptex->height;
				rxe = rxe / (GLfloat)ptex->width;
				rye = rye / (GLfloat)ptex->height;
			}
			GLint rdx = crect.x1;
			GLint rdy = ps->root_height - crect.y1;
			GLint rdxe = rdx + (crect.x2 - crect.x1);
			GLint rdye = rdy - (crect.y2 - crect.y1);

			// Invert Y if needed, this may not work as expected, though. I
			// don't have such a FBConfig to test with.
			if (!ptex->y_inverted) {
				ry = 1.0f - ry;
				rye = 1.0f - rye;
			}

			// log_trace("Rect %d: %f, %f, %f, %f -> %d, %d, %d, %d", ri, rx,
			// ry, rxe, rye,
			//          rdx, rdy, rdxe, rdye);

#define P_TEXCOORD(cx, cy)                                                               \
	{                                                                                \
		if (dual_texture) {                                                      \
			glMultiTexCoord2f(GL_TEXTURE0, cx, cy);                          \
			glMultiTexCoord2f(GL_TEXTURE1, cx, cy);                          \
		} else                                                                   \
			glTexCoord2f(cx, cy);                                            \
	}
			P_TEXCOORD(rx, ry);
			glVertex3i(rdx, rdy, z);

			P_TEXCOORD(rxe, ry);
			glVertex3i(rdxe, rdy, z);

			P_TEXCOORD(rxe, rye);
			glVertex3i(rdxe, rdye, z);

			P_TEXCOORD(rx, rye);
			glVertex3i(rdx, rdye, z);
		}
		P_PAINTREG_END();
	}

	// Cleanup
	glBindTexture(ptex->target, 0);
	glColor4f(0.0f, 0.0f, 0.0f, 0.0f);
	glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
	glDisable(GL_BLEND);
	glDisable(GL_COLOR_LOGIC_OP);
	glDisable(ptex->target);

	if (dual_texture) {
		glActiveTexture(GL_TEXTURE1);
		glBindTexture(ptex->target, 0);
		glDisable(ptex->target);
		glActiveTexture(GL_TEXTURE0);
	}

	if (has_prog)
		glUseProgram(0);

	gl_check_err();

	return true;
}