[core] Bind only active attributes in order to avoid exceeding attribute limits (#9373)

Introducing two new attributes to enable property functions for line-width (#9250) pushed the attribute count over GL_MAX_VERTEX_ATTRIBS on some devices. Now we selectively bind only attributes that are used, making it unlikely to surpass GL_MAX_VERTEX_ATTRIBS.

1 files changed, 46 insertions, 0 deletions

diff --git a/src/mbgl/gl/attribute.cpp b/src/mbgl/gl/attribute.cpp
index e05ca75866..4e6f78e689 100644
--- a/src/mbgl/gl/attribute.cpp
+++ b/src/mbgl/gl/attribute.cpp
@@ -2,14 +2,55 @@
 #include <mbgl/gl/context.hpp>
 #include <mbgl/gl/gl.hpp>
 
+#include <cstring>
+
 namespace mbgl {
 namespace gl {
 
 AttributeLocation bindAttributeLocation(ProgramID id, AttributeLocation location, const char* name) {
+    assert(location < 8);
     MBGL_CHECK_ERROR(glBindAttribLocation(id, location, name));
     return location;
 }
 
+int32_t getActiveAttributeCount(ProgramID id) {
+    GLint numAttributes;
+    MBGL_CHECK_ERROR(glGetProgramiv(id, GL_ACTIVE_ATTRIBUTES, &numAttributes));
+    return numAttributes;
+}
+
+int32_t getMaxAttributeNameLength(ProgramID id) {
+    GLint nameLength;
+    MBGL_CHECK_ERROR(glGetProgramiv(id, GL_ACTIVE_ATTRIBUTE_MAX_LENGTH, &nameLength));
+    return nameLength;
+}
+
+std::string getAttributeName(ProgramID id, int32_t maxLength, AttributeLocation location) {
+    std::string attributeName;
+    attributeName.resize(maxLength);
+    GLsizei actualLength;
+    GLint size;
+    GLenum type;
+    MBGL_CHECK_ERROR(glGetActiveAttrib(id, static_cast<GLuint>(location),
+                                       static_cast<GLsizei>(maxLength), &actualLength, &size, &type,
+                                       const_cast<char*>(attributeName.data())));
+    attributeName.resize(actualLength);
+    return attributeName;
+}
+
+std::set<std::string> getActiveAttributes(ProgramID id) {
+    std::set<std::string> activeAttributes;
+
+    GLint attributeCount = getActiveAttributeCount(id);
+    GLint maxAttributeLength = getMaxAttributeNameLength(id);
+
+    for (int32_t i = 0; i < attributeCount; i++) {
+        activeAttributes.emplace(getAttributeName(id, maxAttributeLength, i));
+    }
+
+    return activeAttributes;
+}
+
 void DisabledAttribute::bind(Context&, AttributeLocation location, std::size_t) const {
     MBGL_CHECK_ERROR(glDisableVertexAttribArray(location));
 }
@@ -25,6 +66,11 @@ template <> DataType DataTypeOf<float>    = DataType::Float;
 
 template <class T, std::size_t N>
 void AttributeBinding<T, N>::bind(Context& context, AttributeLocation location, std::size_t vertexOffset) const {
+    // FillProgram will attempt to bind at location -1 because it includes
+    // a fill-outline-color paint property but does not use it or have an
+    // a_outline_color shader attribute - in this case, we have nothing to bind.
+    if (location == -1) return;
+
     context.vertexBuffer = vertexBuffer;
     MBGL_CHECK_ERROR(glEnableVertexAttribArray(location));
     MBGL_CHECK_ERROR(glVertexAttribPointer(