#include "dither_effect.h"
#include "effect_util.h"
+#include "init.h"
#include "util.h"
namespace {
std::string DitherEffect::output_fragment_shader()
{
- return read_file("dither_effect.frag");
+ char buf[256];
+ sprintf(buf, "#define NEED_EXPLICIT_ROUND %d\n", (movit_num_wrongly_rounded > 0));
+ return buf + read_file("dither_effect.frag");
}
void DitherEffect::update_texture(GLuint glsl_program_num, const std::string &prefix, unsigned *sampler_num)
// we don't have to worry about it.
float tc_scale[] = { float(width) / float(texture_width), float(height) / float(texture_height) };
set_uniform_vec2(glsl_program_num, prefix, "tc_scale", tc_scale);
+
+ // Used if the shader needs to do explicit rounding.
+ int round_fac = (1 << num_bits) - 1;
+ set_uniform_float(glsl_program_num, prefix, "round_fac", round_fac);
+ set_uniform_float(glsl_program_num, prefix, "inv_round_fac", 1.0f / round_fac);
}
uniform sampler2D PREFIX(dither_tex);
uniform vec2 PREFIX(tc_scale);
+uniform float PREFIX(round_fac), PREFIX(inv_round_fac);
vec4 FUNCNAME(vec2 tc) {
// We also choose to dither alpha, just in case.
// Maybe it should in theory have a separate dither,
- // but I doubt it matters much. We currently don't
- // really handle alpha in any case.
- return INPUT(tc) + texture2D(PREFIX(dither_tex), tc * PREFIX(tc_scale)).xxxx;
+ // but I doubt it matters much.
+ vec4 result = INPUT(tc) + texture2D(PREFIX(dither_tex), tc * PREFIX(tc_scale)).xxxx;
+
+ // NEED_EXPLICIT_ROUND will be #defined to 1 if the GPU has inaccurate
+ // fp32 -> int8 framebuffer rounding, and 0 otherwise.
+#if NEED_EXPLICIT_ROUND
+ result = round(result * vec4(PREFIX(round_fac))) * vec4(PREFIX(inv_round_fac));
+#endif
+
+ return result;
}
MovitDebugLevel movit_debug_level = MOVIT_DEBUG_ON;
float movit_texel_subpixel_precision;
bool movit_srgb_textures_supported;
+int movit_num_wrongly_rounded;
// The rules for objects with nontrivial constructors in static scope
// are somewhat convoluted, and easy to mess up. We simply have a
check_error();
}
+void measure_roundoff_problems()
+{
+ // Generate a destination texture to render to, and an FBO.
+ GLuint dst_texnum, fbo;
+
+ glGenTextures(1, &dst_texnum);
+ check_error();
+ glBindTexture(GL_TEXTURE_2D, dst_texnum);
+ check_error();
+ glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, 512, 1, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
+ check_error();
+
+ glGenFramebuffers(1, &fbo);
+ check_error();
+ glBindFramebuffer(GL_FRAMEBUFFER, fbo);
+ check_error();
+ glFramebufferTexture2D(
+ GL_FRAMEBUFFER,
+ GL_COLOR_ATTACHMENT0,
+ GL_TEXTURE_2D,
+ dst_texnum,
+ 0);
+ check_error();
+
+ // Now generate a texture where every value except the last should be
+ // rounded up to the next one. However, there are cards (in highly
+ // common use) that can't do this right, for unknown reasons.
+ GLuint src_texnum;
+ float texdata[512];
+ for (int i = 0; i < 256; ++i) {
+ texdata[i * 2 + 0] = (i + 0.48) / 255.0;
+ texdata[i * 2 + 1] = (i + 0.52) / 255.0;
+ }
+ glGenTextures(1, &src_texnum);
+ check_error();
+ glBindTexture(GL_TEXTURE_1D, src_texnum);
+ check_error();
+ glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
+ check_error();
+ glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+ check_error();
+ glTexImage1D(GL_TEXTURE_1D, 0, GL_LUMINANCE32F_ARB, 512, 0, GL_LUMINANCE, GL_FLOAT, texdata);
+ check_error();
+ glEnable(GL_TEXTURE_1D);
+ check_error();
+
+ // Basic state.
+ glDisable(GL_BLEND);
+ check_error();
+ glDisable(GL_DEPTH_TEST);
+ check_error();
+ glDepthMask(GL_FALSE);
+ check_error();
+
+ glViewport(0, 0, 512, 1);
+
+ glMatrixMode(GL_PROJECTION);
+ glLoadIdentity();
+ glOrtho(0.0, 1.0, 0.0, 1.0, 0.0, 1.0);
+
+ glMatrixMode(GL_MODELVIEW);
+ glLoadIdentity();
+ check_error();
+
+ // Draw the texture stretched over a long quad, interpolating it out.
+ glBegin(GL_QUADS);
+
+ glTexCoord1f(0.0f);
+ glVertex2f(0.0f, 0.0f);
+
+ glTexCoord1f(1.0f);
+ glVertex2f(1.0f, 0.0f);
+
+ glTexCoord1f(1.0f);
+ glVertex2f(1.0f, 1.0f);
+
+ glTexCoord1f(0.0f);
+ glVertex2f(0.0f, 1.0f);
+
+ glEnd();
+ check_error();
+
+ glDisable(GL_TEXTURE_1D);
+ check_error();
+
+ // Now read the data back and see what the card did. (Ignore the last value.)
+ // (We only look at the red channel; the others will surely be the same.)
+ unsigned char out_data[512];
+ glReadPixels(0, 0, 512, 1, GL_RED, GL_UNSIGNED_BYTE, out_data);
+ check_error();
+
+ int wrongly_rounded = 0;
+ for (unsigned i = 0; i < 255; ++i) {
+ if (out_data[i * 2 + 0] != i) {
+ ++wrongly_rounded;
+ }
+ if (out_data[i * 2 + 1] != i + 1) {
+ ++wrongly_rounded;
+ }
+ }
+
+ movit_num_wrongly_rounded = wrongly_rounded;
+
+ // Clean up.
+ glBindTexture(GL_TEXTURE_1D, 0);
+ check_error();
+ glBindFramebuffer(GL_FRAMEBUFFER, 0);
+ check_error();
+ glDeleteFramebuffers(1, &fbo);
+ check_error();
+ glDeleteTextures(1, &dst_texnum);
+ check_error();
+ glDeleteTextures(1, &src_texnum);
+ check_error();
+}
+
void check_extensions()
{
// We fundamentally need FBOs and floating-point textures.
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
measure_texel_subpixel_precision();
+ measure_roundoff_problems();
check_extensions();
movit_initialized = true;
// We currently don't bother to test for more than 1024 levels.
extern float movit_texel_subpixel_precision;
+// Some GPUs use very inaccurate fixed-function circuits for rounding
+// floating-point values to 8-bit outputs, leading to absurdities like
+// the roundoff point between 128 and 129 being 128.62 instead of 128.6.
+// We test, for every integer, x+0.48 and x+0.52 and check that they
+// round the right way (giving some leeway, but not a lot); the number
+// of errors are stored here.
+//
+// If this value is above 0, and you have enabled dithering, we will
+// round off explicitly at the very end of the shader.
+extern int movit_num_wrongly_rounded;
+
// Whether the GPU in use supports GL_EXT_texture_sRGB.
extern bool movit_srgb_textures_supported;