[Fix, Perf, Test] (MG_State, MG_Impl/GLImpl, MG_Test, MG_IntegrationTest): a pipeline composite mirrors only the uniforms a stage was written to, and survives a sampler or block rebinding

This commit is contained in:
2026-08-11 23:11:13 -04:00
parent ef4c6dbe0a
commit ff324057ad
8 changed files with 894 additions and 36 deletions
@@ -599,6 +599,241 @@ void main() { o_color = u_colour; }
gl.EndFrame();
}
// The shared-header idiom, drawn: BOTH stages declare `u_mvp` because they both include the
// same header, and only the VERTEX program is ever written to.
//
// The composite has one slot for `u_mvp`, and mirroring every active uniform of every stage
// in stage order meant the fragment program's untouched zero matrix landed last and won.
// The vertex stage then transformed every vertex by a zero matrix and the frame came out
// empty - from an application that had done nothing wrong, with no GL error anywhere to say
// so. Only uniforms a stage has actually been written to are mirrored now.
TEST_F(ProgramPipelineScenario, AUniformDeclaredInTwoStagesKeepsTheValueTheWrittenStageHolds) {
if (!Ready()) return;
HeadlessGL& gl = Gl();
const int width = gl.Width();
const int height = gl.Height();
// The same declaration in both stages, exactly as a shared header produces it. The
// fragment stage does not even USE it for its output - declaring it is enough.
static const char* kSharedMvpVS = R"(#version 430 core
out gl_PerVertex { vec4 gl_Position; };
uniform mat4 u_mvp;
void main()
{
vec4 corner = vec4(0.0, 0.0, 0.0, 1.0);
switch (gl_VertexID)
{
case 0: corner = vec4(-1.0, -1.0, 0.0, 1.0); break;
case 1: corner = vec4( 1.0, -1.0, 0.0, 1.0); break;
case 2: corner = vec4(-1.0, 1.0, 0.0, 1.0); break;
case 3: corner = vec4( 1.0, 1.0, 0.0, 1.0); break;
}
gl_Position = u_mvp * corner;
}
)";
static const char* kSharedMvpFS = R"(#version 430 core
uniform mat4 u_mvp;
out vec4 o_color;
void main() { o_color = vec4(0.0, 1.0, 0.0, u_mvp[3][3]); }
)";
const GLuint vs = MakeSeparable(GL_VERTEX_SHADER, kSharedMvpVS);
const GLuint fs = MakeSeparable(GL_FRAGMENT_SHADER, kSharedMvpFS);
if (vs == 0 || fs == 0) return;
const GLuint pipeline = MakePipeline();
glUseProgramStages(pipeline, GL_VERTEX_SHADER_BIT, vs);
glUseProgramStages(pipeline, GL_FRAGMENT_SHADER_BIT, fs);
glBindProgramPipeline(pipeline);
// Written through the VERTEX program only - which is the whole point. The fragment
// program's `u_mvp` is left at GL's zero default and must not win the composite's slot.
glActiveShaderProgram(pipeline, vs);
const GLint location = glGetUniformLocation(vs, "u_mvp");
ASSERT_NE(location, -1);
const GLfloat identity[16] = {1.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f,
0.0f, 0.0f, 1.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f};
glUniformMatrix4fv(location, 1, GL_FALSE, identity);
ASSERT_EQ(FirstGLError(), 0u) << "glUniformMatrix4fv through the active shader program errored";
GLuint vao = 0;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
BindDefaultFramebuffer();
glViewport(0, 0, width, height);
glDisable(GL_SCISSOR_TEST);
glDisable(GL_DEPTH_TEST);
ClearTo(0.0f, 0.0f, 0.0f, 1.0f);
glUseProgram(0);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
// A zero matrix collapses all four corners onto the origin and paints nothing at all, so
// "green over the whole viewport" IS the assertion that the written matrix was the one
// the draw used. (The fragment stage reads u_mvp too - into the alpha channel - purely
// so the optimizer cannot delete its declaration and make the case vacuous.)
const Image painted = ReadPixels(width, height);
EXPECT_TRUE(RegionIsMostly(painted, 2, width - 3, 2, height - 3, "green", 0.0,
"a pipeline whose u_mvp is declared in both stages and written in one"));
EXPECT_EQ(FirstGLError(), 0u) << "the shared-uniform pipeline draw leaked a GL error";
glBindVertexArray(0);
glDeleteVertexArrays(1, &vao);
gl.EndFrame();
}
// Rebinding a uniform block AFTER the pipeline has already drawn once.
//
// This is the shape the composite cache key change put weight on. The composite used to be
// thrown away and relinked whenever glUniformBlockBinding moved a stage program's backend
// state version, so the second draw here got a brand-new composite that happened to pick the
// new binding up on the way. Now the composite SURVIVES the rebinding, which means the only
// thing that can carry the new binding to the draw is the refresh path - so this case is
// what says that path is really doing the work.
TEST_F(ProgramPipelineScenario, RebindingAUniformBlockBetweenDrawsReachesTheNextDraw) {
if (!Ready()) return;
HeadlessGL& gl = Gl();
const int width = gl.Width();
const int height = gl.Height();
static const char* kUniformBlockFS = R"(#version 430 core
layout(std140) uniform Colour { vec4 u_colour; };
out vec4 o_color;
void main() { o_color = u_colour; }
)";
const GLuint vs = MakeSeparable(GL_VERTEX_SHADER, kSeparableVS);
const GLuint fs = MakeSeparable(GL_FRAGMENT_SHADER, kUniformBlockFS);
if (vs == 0 || fs == 0) return;
// Two buffers on two different binding points, holding two different colours.
const GLfloat red[4] = {1.0f, 0.0f, 0.0f, 1.0f};
const GLfloat green[4] = {0.0f, 1.0f, 0.0f, 1.0f};
constexpr GLuint kFirstBinding = 2;
constexpr GLuint kSecondBinding = 5;
GLuint buffers[2] = {0, 0};
glGenBuffers(2, buffers);
glBindBuffer(GL_UNIFORM_BUFFER, buffers[0]);
glBufferData(GL_UNIFORM_BUFFER, sizeof(red), red, GL_STATIC_DRAW);
glBindBufferBase(GL_UNIFORM_BUFFER, kFirstBinding, buffers[0]);
glBindBuffer(GL_UNIFORM_BUFFER, buffers[1]);
glBufferData(GL_UNIFORM_BUFFER, sizeof(green), green, GL_STATIC_DRAW);
glBindBufferBase(GL_UNIFORM_BUFFER, kSecondBinding, buffers[1]);
glBindBuffer(GL_UNIFORM_BUFFER, 0);
const GLuint blockIndex = glGetUniformBlockIndex(fs, "Colour");
ASSERT_NE(blockIndex, GL_INVALID_INDEX);
glUniformBlockBinding(fs, blockIndex, kFirstBinding);
const GLuint pipeline = MakePipeline();
glUseProgramStages(pipeline, GL_VERTEX_SHADER_BIT, vs);
glUseProgramStages(pipeline, GL_FRAGMENT_SHADER_BIT, fs);
GLuint vao = 0;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
BindDefaultFramebuffer();
glViewport(0, 0, width, height);
glDisable(GL_SCISSOR_TEST);
glDisable(GL_DEPTH_TEST);
glUseProgram(0);
glBindProgramPipeline(pipeline);
// Draw one: the composite is built here, against binding 2.
ClearTo(0.0f, 0.0f, 0.0f, 1.0f);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
const Image first = ReadPixels(width, height);
EXPECT_TRUE(RegionIsMostly(first, 2, width - 3, 2, height - 3, "red", 0.0,
"the first pipeline draw, with Colour on binding 2"));
ASSERT_EQ(FirstGLError(), 0u) << "the first uniform-block pipeline draw leaked a GL error";
// Move the block to the other binding point, with the composite already built and cached.
glUniformBlockBinding(fs, blockIndex, kSecondBinding);
ASSERT_EQ(FirstGLError(), 0u) << "rebinding a uniform block between draws errored";
// Draw two must read the OTHER buffer.
ClearTo(0.0f, 0.0f, 0.0f, 1.0f);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
const Image second = ReadPixels(width, height);
EXPECT_TRUE(RegionIsMostly(second, 2, width - 3, 2, height - 3, "green", 0.0,
"the second pipeline draw, after Colour was rebound to binding 5"));
EXPECT_EQ(FirstGLError(), 0u) << "the rebound uniform-block pipeline draw leaked a GL error";
glBindVertexArray(0);
glDeleteVertexArrays(1, &vao);
glDeleteBuffers(2, buffers);
gl.EndFrame();
}
// The sampler-unit half of the same question, in a loop: set a unit, draw, repeat. This is
// the shape KHR-GL42.shader_image_load_store.advanced-sso-* and the compute_shader SSO cases
// run, and the one that used to relink the composite on every single iteration. The pixels
// pin what the loop must PRODUCE; the composite-identity assertion that pins what it must
// COST lives in the MG_Test unit suite, where the object itself is reachable.
TEST_F(ProgramPipelineScenario, ASamplerUnitRewrittenBetweenDrawsKeepsPaintingTheRightTexture) {
if (!Ready()) return;
HeadlessGL& gl = Gl();
const int width = gl.Width();
const int height = gl.Height();
static const char* kSamplerFS = R"(#version 430 core
uniform sampler2D u_tex;
out vec4 o_color;
void main() { o_color = texture(u_tex, vec2(0.5)); }
)";
const GLuint vs = MakeSeparable(GL_VERTEX_SHADER, kSeparableVS);
const GLuint fs = MakeSeparable(GL_FRAGMENT_SHADER, kSamplerFS);
if (vs == 0 || fs == 0) return;
// One texture per unit, each a different solid colour, so the pixels say which unit the
// draw actually sampled.
constexpr int kUnits = 4;
const GLubyte colours[kUnits][4] = {{255, 0, 0, 255}, {0, 255, 0, 255}, {0, 0, 255, 255}, {255, 255, 0, 255}};
const char* names[kUnits] = {"red", "green", "blue", "yellow"};
GLuint textures[kUnits] = {};
glGenTextures(kUnits, textures);
for (int unit = 0; unit < kUnits; ++unit) {
glActiveTexture(GL_TEXTURE0 + unit);
glBindTexture(GL_TEXTURE_2D, textures[unit]);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, 1, 1, 0, GL_RGBA, GL_UNSIGNED_BYTE, colours[unit]);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
}
glActiveTexture(GL_TEXTURE0);
ASSERT_EQ(FirstGLError(), 0u) << "texture setup left a GL error behind";
const GLuint pipeline = MakePipeline();
glUseProgramStages(pipeline, GL_VERTEX_SHADER_BIT, vs);
glUseProgramStages(pipeline, GL_FRAGMENT_SHADER_BIT, fs);
glBindProgramPipeline(pipeline);
glActiveShaderProgram(pipeline, fs);
const GLint sampler = glGetUniformLocation(fs, "u_tex");
ASSERT_NE(sampler, -1);
GLuint vao = 0;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
BindDefaultFramebuffer();
glViewport(0, 0, width, height);
glDisable(GL_SCISSOR_TEST);
glDisable(GL_DEPTH_TEST);
glUseProgram(0);
for (int unit = 0; unit < kUnits; ++unit) {
glUniform1i(sampler, unit);
ClearTo(0.0f, 0.0f, 0.0f, 1.0f);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
const Image painted = ReadPixels(width, height);
EXPECT_TRUE(RegionIsMostly(painted, 2, width - 3, 2, height - 3, names[unit], 0.0,
"a pipeline draw after its sampler was pointed at another unit"))
<< "unit " << unit;
EXPECT_EQ(FirstGLError(), 0u) << "the sampler-rewrite pipeline draw leaked a GL error at unit " << unit;
}
glBindVertexArray(0);
glDeleteVertexArrays(1, &vao);
glDeleteTextures(kUnits, textures);
gl.EndFrame();
}
// build-separable / build-monolithic reduce to this: a separable program and a monolithic one
// must both be usable, and switching between pipeline and glUseProgram must leave no error.
TEST_F(ProgramPipelineScenario, SwitchingBetweenAPipelineAndAMonolithicProgramLeavesNoError) {