config: add tweak.min-stride-alignment

This allows the user to configure the value by which a surface
buffer's stride must be an even multiple of.

This can be used to ensure the stride meets the GPU driver's
requirements for direct import.

Defaults to 256. Set to 0 to disable.

Closes #2182

config.c

@@ -2848,6 +2848,10 @@ parse_section_tweak(struct context *ctx)
 #endif
     }
 
+    else if (streq(key, "min-stride-alignment")) {
+        return value_to_uint32(ctx, 10, &conf->tweak.min_stride_alignment);
+    }
+
     else {
         LOG_CONTEXTUAL_ERR("not a valid option: %s", key);
         return false;
@@ -3496,6 +3500,7 @@ config_load(struct config *conf, const char *conf_path,
             .font_monospace_warn = true,
             .sixel = true,
             .surface_bit_depth = SHM_BITS_AUTO,
+            .min_stride_alignment = 256,
         },
 
         .touch = {

config.h

@@ -435,6 +435,7 @@ struct config {
         bool font_monospace_warn;
         bool sixel;
         enum shm_bit_depth surface_bit_depth;
+        uint32_t min_stride_alignment;
     } tweak;
 
     struct {

main.c

@@ -597,6 +597,7 @@ main(int argc, char *const *argv)
     }
 
     shm_set_max_pool_size(conf.tweak.max_shm_pool_size);
+    shm_set_min_stride_alignment(conf.tweak.min_stride_alignment);
 
     if ((fdm = fdm_init()) == NULL)
         goto out;

shm.c

@@ -13,7 +13,6 @@
 
 #include <pixman.h>
 
-#include <fcft/stride.h>
 #include <tllist.h>
 
 #define LOG_MODULE "shm"
@@ -21,6 +20,7 @@
 #include "log.h"
 #include "debug.h"
 #include "macros.h"
+#include "stride.h"
 #include "xmalloc.h"
 
 #if !defined(MAP_UNINITIALIZED)
@@ -61,6 +61,8 @@ static off_t max_pool_size = 512 * 1024 * 1024;
 static bool can_punch_hole = false;
 static bool can_punch_hole_initialized = false;
 
+static size_t min_stride_alignment = 0;
+
 struct buffer_pool {
     int fd;                /* memfd */
     struct wl_shm_pool *wl_pool;
@@ -113,6 +115,12 @@ shm_set_max_pool_size(off_t _max_pool_size)
     max_pool_size = _max_pool_size;
 }
 
+void
+shm_set_min_stride_alignment(size_t _min_stride_alignment)
+{
+    min_stride_alignment = _min_stride_alignment;
+}
+
 static void
 buffer_destroy_dont_close(struct buffer *buf)
 {
@@ -342,6 +350,13 @@ get_new_buffers(struct buffer_chain *chain, size_t count,
                 ? chain->pixman_fmt_with_alpha
                 : chain->pixman_fmt_without_alpha,
             widths[i]);
+
+        if (min_stride_alignment > 0) {
+            const size_t m = min_stride_alignment;
+            stride[i] = (stride[i] + m - 1) / m * m;
+        }
+
+        xassert(min_stride_alignment == 0 || stride[i] % min_stride_alignment == 0);
         sizes[i] = stride[i] * heights[i];
         total_size += sizes[i];
     }

shm.h

@@ -42,7 +42,10 @@ struct buffer {
 };
 
 void shm_fini(void);
+
+/* TODO: combine into shm_init() */
 void shm_set_max_pool_size(off_t max_pool_size);
+void shm_set_min_stride_alignment(size_t min_stride_alignment);
 
 struct buffer_chain;
 struct buffer_chain *shm_chain_new(

tests/test-config.c

@@ -1413,6 +1413,9 @@ test_section_tweak(void)
     test_float(&ctx, &parse_section_tweak, "bold-text-in-bright-amount",
                &conf.bold_in_bright.amount);
 
+    test_uint32(&ctx, &parse_section_tweak, "min-stride-alignment",
+                &conf.tweak.min_stride_alignment);
+
 #if 0 /* Must be equal to, or less than INT32_MAX */
     test_uint32(&ctx, &parse_section_tweak, "max-shm-pool-size-mb",
                 &conf.tweak.max_shm_pool_size);