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gdkgl: Texture quads in one giant draw call

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This requires us to use GL_TRIANGLES and six verts per quad instead
of four, which makes me think it might not be worth it on
well-optimized GL drivers. However, from talking to some driver
developers about it, the GL_TRIANGLES should be faster, since this
means that there's one giant contiguous buffer instead of many small
buffers.

If we were really rendering a lot of quads, I'd use an element buffer
and GL_PRIMITIVE_RESTART, but we're really not ever rendering that
many quads, and the setup cost for that would just be too annoying.
This commit is contained in:
Jasper St. Pierre
2014-11-22 10:17:22 -08:00
parent 6ffba866a6
commit c01e37a9a5
1 changed files with 22 additions and 4 deletions
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26
gdk/gdkgl.c
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@ -24,6 +24,7 @@
#include <epoxy/gl.h>
#include <math.h>
#include <string.h>
static cairo_user_data_key_t direct_key;
@ -217,6 +218,7 @@ gdk_gl_texture_quads (GdkGLContext *paint_context,
float w = gdk_window_get_width (window) * window_scale;
float h = gdk_window_get_height (window) * window_scale;
int i;
float *vertex_buffer_data;
bind_vao (paint_data);
@ -240,20 +242,36 @@ gdk_gl_texture_quads (GdkGLContext *paint_context,
glVertexAttribPointer (program->position_location, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 4, NULL);
glVertexAttribPointer (program->uv_location, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 4, NULL + sizeof(float) * 2);
#define VERTEX_SIZE 4
#define QUAD_N_VERTICES 6
#define QUAD_SIZE (VERTEX_SIZE * QUAD_N_VERTICES)
vertex_buffer_data = g_new (float, n_quads * QUAD_SIZE);
for (i = 0; i < n_quads; i++)
{
GdkTexturedQuad *quad = &quads[i];
float vertex_buffer_data[] = {
float vertex_data[] = {
(quad->x1 * 2) / w - 1, (quad->y1 * 2) / h - 1, quad->u1, quad->v1,
(quad->x1 * 2) / w - 1, (quad->y2 * 2) / h - 1, quad->u1, quad->v2,
(quad->x2 * 2) / w - 1, (quad->y1 * 2) / h - 1, quad->u2, quad->v1,
(quad->x2 * 2) / w - 1, (quad->y2 * 2) / h - 1, quad->u2, quad->v2,
(quad->x1 * 2) / w - 1, (quad->y2 * 2) / h - 1, quad->u1, quad->v2,
(quad->x1 * 2) / w - 1, (quad->y1 * 2) / h - 1, quad->u1, quad->v1,
(quad->x2 * 2) / w - 1, (quad->y1 * 2) / h - 1, quad->u2, quad->v1,
};
glBufferData (GL_ARRAY_BUFFER, sizeof(vertex_buffer_data), vertex_buffer_data, GL_STREAM_DRAW);
glDrawArrays (GL_TRIANGLE_FAN, 0, 4);
float *vertex = &vertex_buffer_data[i * QUAD_SIZE];
memcpy (vertex, vertex_data, sizeof(vertex_data));
}
glBufferData (GL_ARRAY_BUFFER, sizeof(float) * n_quads * QUAD_SIZE, vertex_buffer_data, GL_STREAM_DRAW);
glDrawArrays (GL_TRIANGLES, 0, n_quads * QUAD_N_VERTICES);
g_free (vertex_buffer_data);
glDisableVertexAttribArray (0);
glDisableVertexAttribArray (1);
}